Bone marrow in horses is a spongy tissue found within the cavities of certain bones, such as the pelvis, ribs, and femur. It is a vital component of the hematopoietic system, responsible for the production of blood cells, including red blood cells, white blood cells, and platelets. These cells are crucial for oxygen transport, immune function, and blood clotting, respectively. Bone marrow consists of two types: red marrow, which is actively involved in blood cell production, and yellow marrow, which primarily stores fat. The composition and activity of bone marrow can change with age, health status, and physiological demands. This page compiles peer-reviewed research studies and scholarly articles that explore the structure, function, and clinical implications of bone marrow in equine health and disease.
Scocchi M, Bontempo D, Boscolo S, Tomasinsig L, Giulotto E, Zanetti M.Cathelicidins are precursors of defense peptides of the innate immunity and are widespread in mammals. Their structure comprises a conserved prepropiece and an antimicrobial domain that is structurally varied both intra- and inter-species. We investigated the complexity of the cathelicidin family in horse by a reverse transcription-PCR-based cloning strategy of myeloid mRNA and by Southern and Western analyses. Three novel cathelicidin sequences were deduced from bone marrow mRNA and designated equine cathelicidins eCATH-1, eCATH-2 and eCATH-3. Putative antimicrobial domains of 26, 27 and 40 r...
Savage CJ.Nomenclature regarding neoplasia of the hematopoietic and lymphoid tissues in the horse is confusing. This article will clarify terminology, and discuss the individual lymphoproliferative and myeloproliferative disorders recognized in the horse. Diagnostic techniques that are useful in cases in which hematopoietic or lymphoid tissue neoplasia are suspected include histochemical staining profiles, bone marrow aspiration, and bone marrow biopsy.
Geissbühler U, Busato A, Ueltschi G.Obtaining high-quality radiographs of the proximal aspect of equine limbs is difficult because of the large muscles in these regions. The use of scintigraphy may provide further information. Abnormal bone scan findings of the ischial tuberosity or the third trochanter were found in 29 adult horses with obscure hind limb lameness between 1986 and 1996 at the Large Animal Clinic of the University of Bern. Each had abnormal radiopharmaceutical uptake but not all had radiographic changes. Radiopharmaceutical uptake ratios between the ischial tuberosity and the greater trochanter were calculated. T...
Gray AW, Davies ME, Jeffcott LB.We report on preliminary results of a novel in vitro culture system designed to generate equine osteoclasts in large numbers. Osteoclast generation, as determined by the expression of tartrate resistant acid phosphatase (TRAP) and ability to resorb bone, was enhanced in equine bone marrow cultures supplemented with fibroblastic cell (L929) conditioned medium (L929-CM). Bone marrow was collected from a total of 12 horses and ponies and TRAP-positive cells with bone resorbing ability were generated in significant numbers in the last seven. TRAP-positive mononuclear cells appeared after three day...
Fortier LA, Nixon AJ, Williams J, Cable CS.To isolate mesenchymal stem cells from adult horses and determine specific monolayer culture conditions required to enhance biochemically and phenotypically defined chondrocytic differentiation. Methods: 2 adult horse bone marrow donors without skeletal or hematologic abnormalities. Methods: Bone marrow was aspirated from the sternebra, and mesenchymal stem cells were isolated by centrifugation and cultured in monolayers. Subcultures were established in 24-well plates on day 13. Culture medium was harvested every 2 days, and culture of 12 of the 24 wells was terminated on day 6 and of the rema...
Pearce SG, Firth EC, Grace ND, Fennessy PF.The effect of copper status on the evidence of bone and cartilage lesions was investigated in 21 Thoroughbred foals. The foals and their dams were grazed on pasture containing 4.4-8.6 mg Cu/kg dry matter (DM). Four treatment groups were created by randomly allocating mares and their foals to either copper supplemented (0.5 mg Cu/kg liveweight (LW)/day), or control (pasture only) groups. This experimental design allowed the effect of copper supplementation of mare and foal to be examined independently. Parameters of bone and cartilage development were assessed in the foals both in vivo, and at ...
Toribio RE, Bain FT, Mrad DR, Messer NT, Sellers RS, Hinchcliff KW.Three weak, recumbent neonatal foals with skin lesions, including a thin wooly coat, were born to mares being treated for equine protozoal myeloencephalitis. Mares received sulfadiazine or sulfamethoxazole-trimethoprim, pyrimethamine, folic acid, and vitamin E orally. Foals were anemic, leukopenic, azotemic, hyponatremic, and hyperkalemic. Serum folate concentrations in the 3 foals and 2 mares were lower than those reported in the literature for clinically normal brood mares. Treatment was unsuccessful. For each foal, necropsy revealed lobulated kidneys with thin cortices and a pale medulla, a...
Scholes SF, Holliman A, May PD, Holmes MA.Fell pony foals developed a syndrome of anaemia, immunodeficiency and peripheral ganglionopathy. They became ill in the second or third week, and died in the second or third month of life. Clinical and pathological investigations revealed severe anaemia associated with small numbers of late erythroid precursors in bone marrow, small thymi, an absence of secondary lymphoid follicles, a lack of plasma cells and neuronal chromatolysis involving trigeminal, cranial mesenteric and dorsal root ganglia. Some of the foals had cryptosporidial enteritis and adenoviral bronchopneumonia and pancreatitis. ...
Kawcak CE, Norrdin RW, Frisbie DD, Trotter GW, Mcilwraith CW.To determine the effects of osteochondral fragmentation and intra-articular corticosteroid treatment on dynamics of bone remodelling and fragility, 12 horses each had a unilateral, 8 mm osteochondral fragment created in the distal aspect of one radiocarpal bone. Six of the horses were treated in the fragmented joint, and the other 6 were treated in the nonfragmented joint with 12 mg of triamcinolone acetonide (TA) 14 and 28 days after surgery. All horses were exercised on a high-speed treadmill starting 15 days, and ending 72 days after surgery. Horses treated with TA in the fragmented joints ...
Tornquist SJ, Oaks JL, Crawford TB.Thrombocytopenia is a common finding in infection with equine infectious anaemia virus (EIAV), a lentivirus with some homology to human immunodeficiency virus (HIV). The thrombocytopenia of EIA, like that in some HIV patients, appears to have a multifactorial pathogenesis. To investigate the decreased platelet production seen in experimental EIA, the levels of three potential negative regulators of platelet production--tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta) and interferon-alpha (IFN-alpha)--were measured in serum and bone marrow of six severe combi...
Piercy RJ, Swardson CJ, Hinchcliff KW.A Standardbred gelding and a colt were examined because of poor performance and anemia. Each horse had been given recombinant human erythropoietin (rhEPO; 4,000 IU) at least twice within the preceding 2 to 4 months. The horses had an Het of 16 and 24%, serum iron concentrations of 210 and 304 micrograms/dl (reference range, 73 to 140 micrograms/dl), total iron binding capacities of 239 and 321 micrograms/dl (reference range, 266 to 364 micrograms/dl), values for the percentage saturation of transferrin by iron of 87.9 and 94% (reference range, 20 to 52%), and serum ferritin concentrations of 2...
Swardson CJ, Lichtenstein DL, Wang S, Montelaro RC, Kociba GJ.To characterize infection of bone marrow-derived macrophages (BMDM) with equine infectious anemia virus (EIAV) by determining virus production, effects on viability, and induction of cytokines. Methods: BMDM obtained from bone marrow of 6 clinically normal adult horses. Methods: BMDM were infected with EIAV at a multiplicity of infection of 8. Cell viability, percentage of cells with detectable viral protein, reverse transcriptase activity, and concentrations of infective virus (focus-forming units/ml), interleukin 6, and tumor necrosis factor-alpha were measured in culture supernatant samples...
Tornquist SJ, Crawford TB.Foals infected with equine infectious anemia virus become thrombocytopenic 7 to 20 days after virus inoculation, and within a few days following the onset of detectable viremia. The thrombocytopenia is associated with suppression of platelet production. Possible mediators of suppression of thrombopoiesis include tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta), cytokines that are released during inflammation. To assess effects of plasma or serum from infected foals on megakaryocyte (MK) growth and maturation in vitro, equine low-density bone marrow cells w...
Ringger NC, Edens L, Bain P, Raskin RE, Larock R.A 5-year-old Thoroughbred mare presented with a 4 week history of weight loss, fever and leukopenia. Rectally, a large active foetus, thickened spleen and an abdominal mass were palpated. Leukopenia, mild anaemia, marked thrombocytopenia and hyperfibrinogenaemia were found. Cytology and cytochemical staining of a bone marrow aspirate supported a diagnosis of acute myelogenous leukaemia. The mare deteriorated despite medical therapy and was humanely euthanased.
Geelen SN, Bernadina WE, Grinwis GC, Kalsbeek HC.A 15-year-old Dutch warmblood mare was presented because of lethargy, which had been present for several weeks, and severe anaemia. Total protein was high and serum electrophoresis revealed a monoclonal peak in the alpha-2 region. Monoclonal immunoglobulin, IgG(T), was detected by immuno-electrophoresis in serum and urine. Postmortem examination revealed a relatively large number of plasmacytoid cells in the bone marrow and a monotonous population of plasmacytoid cells in the spleen. These findings are suggestive of a plasma cell myeloma.
Hawkins DL, Stover SM.To investigate the effect of late gestation, age, and parity on material properties of third metacarpal (MCIII) cortical bone in mares. Methods: 8 healthy mares (treatment group) that died or were euthanatized within 24 hours after parturition because of foaling complications and 6 age-matched, healthy, nonpregnant mares (control group). Methods: After random assignment for mechanical testing and microradiography, the dorsal half of transverse mid-diaphyseal sections of each MCIII bone was divided into lateral, dorsal, and medial regions. Cylinders of bone from each of the 3 regions were teste...
Hornof WJ, Stover SM, Koblik PD, Arthur RM.The research article discusses a study on the use of oblique dorsal views in detecting stress fractures in horses who participate in races. The aim of the researchers was to […]
Jackson B, Eastell R, Russell RG, Lanyon LE, Price JS.For many years total alkaline phosphatase (AP) activity in serum has been used to monitor bone metabolism in different species. However, total AP lacks bone specificity because the total activity in serum is made up of several isoenzymes, of which the liver and bone isoforms predominate. The aim of the present study was to evaluate an immunoradiometric assay for measuring bone specific alkaline phosphatase (BAP) in horses. BAP, a specific marker of bone formation, was measured in sera from thoroughbred horses by using a previously characterised wheat germ lectin (WGL) precipitation assay and a...
Wardrop KJ, Baszler TV, Reilich E, Crawford TB.Morphometric evaluation of bone marrow core biopsies was used to determine megakaryocyte (MK) numbers and MK size in nine foals with equine infectious anemia virus (EIAV)-induced thrombocytopenia. Both immunocompetent normal foals and foals with severe combined immunodeficiency (SCID) were used. Platelet counts were made three times weekly following viral infection. Bone marrow core biopsies were taken from the ilium of each foal prior to experimental infection, immediately after the onset of thrombocytopenia, and at necropsy. All foals developed thrombocytopenia by 23 days postinfection. The ...
Kasza A, Korpula-Mastalerz R, Rose-John S, Dubin A.The horse leucocyte elastase inhibitor (HLEI), present in neutrophils, monocytes and bone marrow cells, is apparently a cytoplasmic protein which is not released from cells even in response to stimulation with lipopolysaccharide, phorbol ester, tumour necrosis factor alpha, interleukin-1 or elastin degradation products. Although no expression of the inhibitor was detected in neutrophils, both monocytes and bone marrow cells were efficient in its synthesis. Using a new expression vector pREST5d, recombinant inhibitor was produced in a large quantity in a soluble form, with a yield of 88 mg per ...
Carlson CS, Cullins LD, Meuten DJ.The objectives of this study were to determine in horses 1) the ages at which viable cartilage canal vessels are present in the articular-epiphyseal cartilage complex of three predilection sites and one nonpredilection site of osteochondrosis (OC), 2) the prevalence of lesions of OC in these sites, and 3) whether there was an association of lesions of OC with necrotic cartilage canal blood vessels. The medial femoral condyle, lateral femoral trochlear ridge, and distal ends of the tibia and proximal phalanx were examined grossly, microradiographically, and histologically in 35 horses 18 months...
Kohn CW, Swardson C, Provost P, Gilbert RO, Couto CG.Myeloid and megakaryocytic bone marrow hypoplasia in association with moderate to profound neutropenia was observed in 8 young Standardbred horses sired by the same stallion; 7 horses were intermittently thrombocytopenic. Evaluation of serial neutrophil counts in 2 horses suggested that a cyclic variation in neutrophil numbers was present, that lymphocyte numbers increased when neutrophil counts decreased, and that platelet counts decreased when neutrophil counts decreased. Preliminary bone marrow cultures indicated that myeloid progenitor cells were present and that these cells were able to r...
Honnas CM, Crabill MR, Mackie JT, Yarbrough TB, Schumacher J.Six horses with septic navicular bursitis or distal sesamoid osteomyelitis were treated by means of surgical debridement and lavage, followed by packing of the wound created in the bottom of the foot with an autogenous cancellous bone graft. Two horses were euthanatized, one 18 months after surgery because of complications in the contralateral support limb, and one 68 days after surgery because of continuing severe lameness. Four horses were alive 9, 16, 21, and 42 months after surgery. One horse was used as a broodmare and did not have observable lameness. Two horses were being ridden. The re...
Zinkl JG, Madigan JE, Fridmann DM, Kabbur MB, Reynal-O'Connor J, Andresen JW.Five Thoroughbred and Quarter Horse cross foals were given 20 micrograms canine recombinant granulocyte-colony stimulating factor (rcG-CSF) per kg bwt intramuscularly (i.m.) on the day of birth and 10 micrograms rcG-CSF/kg for 13 additional days. During this time and for an additional 21 days haematology, bone marrow and clinical chemical analyses were performed. After one day of rcG-CSF administration leucocyte and neutrophil counts increased from 9.16 x 10(9)/l to 23.44 x 10(9)/l and from 6.45 x 10(9)/l to 19.61 x 10(9)/l, respectively. The counts continued to increase for the next 3-4 days ...
Lester GD, Alleman AR, Raskin RE, Meyer JC.Pancytopenia was observed in two 3-year-old geldings and one 11-year-old mare. All horses had a brief history (2 days to 4 weeks) of fever, anorexia, and depression. One of the three horses had blast cells present on a peripheral blood smear. Examination of the bone marrow showed substantial infiltration with neoplastic lymphoid cells. At necropsy, neoplastic cells were restricted to the bone marrow in one horse, present in bone marrow, liver, and spleen in the second horse, and reported in multiple tissues in the third horse, including bone marrow, kidneys, lung, myocardium and lymph nodes. T...
Canè V, Botti P, Soana S.The influence of pulsed low-frequency electromagnetic fields (PEMFs) on bone formation was investigated in studies of the healing process of transcortical holes, bored at the diaphyseal region of metacarpal bones of six adult horses, exposed for 30 days to PEMFs (28 G peak amplitude, 1.3 ms rise time, and 75 Hz repetition rate). A pair of Helmholtz coils, continuously powered by a pulse generator, was applied for 30 days to the left metacarpal bone, through which two holes, of equal diameter and depth, had been bored at the diaphyseal region. Two equal holes, bored at the same level in the rig...
Edwards DF, Parker JW, Wilkinson JE, Helman RG.Plasma cell myelomas in horses have been reported infrequently. Data from 10 cases, 9 from the literature and 1 new case, are used to characterize the disease in the horse. Hot-blooded horses (7/10), specifically Quarter Horses (4/10), were most often affected. Median age at diagnosis was 11 years (range, 3 mo-22 yr) and both male (5) and female horses (5) were represented equally. Clinical findings included weight loss (6/8), anorexia (4/8), fever (4/8), limb edema (4/8), pneumonia (3/8), rear leg paresis/ataxia (3/8), epistaxis (3/8), palpable lymphadenopathy (2/8), and bone pain (2/8). Anem...
Fenger CK, Bertone JJ, Biller D, Merryman J.Generalized medullary infarction of the long bones was diagnosed in a 12-year-old Tennessee Walking Horse mare. The mare was referred after a 6-week course of shifting weight on her hind limbs, and kicking. Physical examination revealed mild stifle joint distention and withdrawal reactions to digital pressure over the long bones. Radiography revealed patchy areas of medullary sclerosis in the distal portion of each femur and proximal portion of each tibia. A full-thickness cortical and cancellous tibial biopsy revealed infarcted bone marrow, with cortical and periosteal osteonecrosis. The caus...
Webb TL, Burnett RC, Avery AC, Olver CS.Characterization of anemia in horses presents a challenge, as they do not release reticulocytes into peripheral blood. Transferrin receptor (TfR) expression is highest on erythroid cells in people and rats, and measurement of a soluble serum form (sTfR) is used to quantify erythropoiesis in these species. We hypothesized that equine TfR (eTfR) expression is similar in quantity and distribution to that in these other species and thus has potential for characterization of the regenerative response in anemic horses. Objective: This study was conducted to clone and sequence the eTfR gene and measu...
Songür M, Şahin E, Demir T, Kalem M, Take Kaplanoğlu G, Altun NŞ.Bone protein extract (BPE) usually requires a carrier or a scaffold for implantation. We aimed to compare the effect of equine-derived BPE, an osteoinductive agent composed of a high amount of type-I collagen and other bone proteins (Colloss-E), with that of human demineralized bone matrix (DBM) for treating cavitary bone defects not requiring scaffold use. Methods: Rabbit distal femoral condyle was used as a stable cavitary bone defect model. Bone defects of 6-mm diameter and 10-12-mm depth were created in the femoral condyles. Rabbits were assigned into the equine-derived BPE (BPE), human-de...
Shaktivesh , Malekipour F, Whitton C, Lee PVS.Standard fatigue testing of bone uses a single load and frequency applied until failure. However, in situ, the subchondral bone of Thoroughbred racehorses is subjected to a combination (or a spectrum) of loads and frequencies during training and racing. Objective: To investigate the use of a fatigue testing method for equine third metacarpal (McIII) subchondral bone under a spectrum of loading conditions which a racehorse is likely to experience during a fast workout. Methods: In vitro biomechanical experimental study. Methods: McIII subchondral bone specimens (n = 12) of racehorses were ha...
Schryver HF, Meakim DW, Lowe JE, Williams J, Soderholm LV, Hintz HF.The effect of level of protein intake on growth and calcium metabolism was studied in 24 foals. Starting at four months old, the foals were fed one of three diets containing all nutrients, with the exception of protein, at levels recommended by the United States National Research Council Subcommittee on Horse Nutrition for a 12 month period. The protein levels in the three diets were 9 per cent (low protein) 14 per cent (NRC recommended level) and 20 per cent (high protein). The foals fed the low protein diet were changed to the high protein diet after 140 days when they were nine months old. ...
Tamura N, Heidari N, Faragher RGA, Smith RKW, Dudhia J.Resveratrol (RSV; trans-3,5,4'-trihydroxystilbene) strongly activates sirtuin 1, and it and its analogue V29 enhance the proliferation of mesenchymal stem/stromal cells (MSCs).Although culture medium containing 5-azacytydine and RSV inhibits senescence of adipose tissue-derived MSCs isolated from horses with metabolic syndrome, few studies have reported the effects of RSV on equine bone marrow-derived MSCs (eBMMSCs) isolated from horses without metabolic syndrome. The aim of this study was to investigate the effects of RSV and V29 on the cell cycle of eBMMSCs. Following treatment with 5 µM RS...
Everett JB, Menarim BC, Barrett SH, Bogers SH, Byron CR, Pleasant RS, Werre SR, Dahlgren LA.Osteoarthritis (OA) can be debilitating and is related to impaired resolution of synovial inflammation. Current treatments offer temporary relief of clinical signs, but have potentially deleterious side effects. Bone marrow mononuclear cells (BMNC) are a rich source of macrophage progenitors that have the ability to reduce OA symptoms in people and inflammation in experimentally-induced synovitis in horses. The objective of this study was to evaluate the ability of intra-articular BMNC therapy to improve clinical signs of naturally occurring equine OA. Horses presenting with clinical and radio...
Faulkner JE, Joostens Z, Broeckx BJG, Hauspie S, Mariën T, Vanderperren K.Sagittal groove disease of the proximal phalanx in equine athletes is commonly considered a bone stress injury. Repetitive hyperextension of the fetlock under high load is thought to contribute to its development. Concurrent changes are often reported in the dorsal sagittal ridge of the third metacarpus/metatarsus (MC3/MT3). Objective: To describe the spectrum of associated osseous abnormalities that are present in the fetlock in a large group of horses diagnosed with sagittal groove disease on low-field magnetic resonance imaging (MRI). Methods: Retrospective, cross-sectional. Methods: MRI im...
Renaudin C, Wensley F, Morgan J, Cassano J, Spriet M.Fetal age in Quarter Horses can be predicted within 2 weeks from 100- to 200- days of gestation using femur length, biparietal diameter (cranium diameter) and eye approximated volume. However, as pregnancy advances, the femur and cranium become too large to be imaged in their entirety using ultrasound and the corresponding biometric parameters can no longer be measured. In this longitudinal study, the proximal phalanx (P1) was evaluated as a novel biometric parameter for late gestation to predict fetal age and bone maturation. Transrectal ultrasound was performed in ten pregnant mares with kno...
Frontiers in geneticsOctober 29, 2024
Volume 15 1455790 doi: 10.3389/fgene.2024.1455790
Harari S, Deretz S, Dumont Saint Priest B, Richard E, Ricard A.In order to find early selection criteria to improve the longevity of show jumping horses, a specific protocol was designed. Unassigned: Before entering competition, young horses selected from extreme stallions for longevity were measured for many traits, including blood parameters. Blood samples were taken from 952 horses aged 2-4 years old, sired by two groups of stallions: one with unfavorable (U) and the other with favorable (F) extreme estimated breeding values for functional longevity. These breeding values were previously calculated from data on 202,320 horses that participated in show...
Beck C, Hitchens PL, Whitton RC.Post-mortem studies have shown that fractures involving the metacarpophalangeal/metatarsophalangeal or fetlock joint are associated with focal areas of microdamage. Identification of computed tomography (CT) features consistent with microdamage and their association with fracture may aid in identification of horses at risk of fracture. Objective: To identify CT features associated with fracture of the metacarpophalangeal/metatarsophalangeal joint. Methods: Retrospective cohort study. Methods: Post-mortem CT images of 367 limbs from 157 Thoroughbred racehorses were graded for CT features. Multi...
Long S, Maleas G, Belacic ZA, Quam VG, Durgam S.To analyze the cellular, growth factor, and cytokine composition of equine sternal bone marrow aspirate (BMA) and laboratory-centrifuged BMA concentrate (BMAC). Unassigned: This was an in vitro experimental study. Cellular composition, growth factors (IGF-I, VEGF, PDGF, TGF-β1), and cytokines (IL-6, IL-10, tumor necrosis factor-α (TNF-α), and IL-1 receptor antagonist protein [IL-1Ra]) were quantified using a standard automated hematology analyzer and ELISA methods, respectively, in donor-matched BMA, BMAC (in-house centrifugation protocol), whole blood, and platelet-rich plasma (E-PET; Pall...
Prasse KW, Lundvall RL, Cheville NF.A newborn foal with multiple, nodular, cutaneous lesions containing mast cells and with mast cell accumulations in bone marrow was observed for 1 year. Cutaneous nodules grew to several centimeters in size, ulcerated, and regressed. Only a few healed nodules remained when the foal was 1 year old. The disease was considered to be similar to urticaria pigmentosa of man.
Sherlock CE, Mair TS, Murray RC, Blunden TS.Emaciated human patients have changes in the fat content in medullary bone that are consistent with serous atrophy of the bone marrow histologically. Serous atrophy has been identified at postmortem examination in horses; however, the magnetic resonance (MR) characteristics have not been documented. Herein we describe the abnormalities of the bone marrow and medullary bone detected by low-field and high-field MR imaging of the distal limbs of three emaciated horses. These low- and high-field MR imaging abnormalities are characterized by a decrease in signal intensity on T1-weighted images in c...
Modransky P, Welker B, Ryan J.A fourth tarsal bone fracture was treated conservatively in an adult draft horse. Seven months after the injury, the horse had no evidence of lameness and was able to compete in athletic events. It has been suggested that conservative management of these fractures be considered for brood animals or animals used for less strenuous activities. The outcome of this case suggests that fourth tarsal bone fractures can be successfully treated in athletic animals with conservative management.
Roberts MC.Progressive leukaemic changes and a persistent anaemia were demonstrated in the blood of a 7 year old gelding, which had shown early signs of lowered performance and unthriftiness, and later developed dependent oedema and became dull and listless. The total leucocyte count, initially within the normal range although reflecting an absolute lymphocytosis, increased fourfold in 6 days from excessive lymphoid production involving predominantly the more immature cell types; lymphoblasts, prolymphocytes and large lymphocytes. The severity of the condition was confirmed by bone marrow biopsy.