Agammaglobulinemia in a horse.

This research explores a case of a young horse with agammaglobulinemia, which is a disorder characterized by lower than regular amounts of immunoglobulin in the blood. The horse, already showing weakness and recurring infections, was found to have critical deficiencies of specific types of immunoglobulins, leading to a diagnosis of this rare disease.

Background and Initial Study

• The case study is centered around an 18-month-old Standardbred horse that had been exhibiting symptoms like persistent fever, multifocal bacterial infections and neutropenia, which is an abnormally low concentration of neutrophils, a type of white blood cell, in the blood.
• The horse also had a significant number of immature neutrophils in the body, leading the researchers to suspect an immunologic deficiency could be the underlying issue.
• After carrying out serum protein electrophoresis, which is a test that can help detect the levels of different proteins in a patient’s serum, the medical team found that the horse had a notably low gamma-globulin fraction, at just 0.2 g for every 100 ml of blood. Gamma globulins play a vital role in the immune system, so this abnormality further indicated an issue with the horse’s immune response.

Identifying Agammaglobulinemia

• To confirm their hypothesis, the researchers carried out additional immunologic testing and histologic examination of the horse’s lymphoid tissues. Histology is the study of the microscopic anatomy of cells and tissues of plants and animals.
• These additional tests led to the identification of the horse’s immune deficit as agammaglobulinemia. This genetic disorder, which leads to an absence or extremely reduced levels of immunoglobulin in the blood, results in increased susceptibility to infections.
• In addition to this, the serum levels of immunoglobulin G and G(T) in the horse, which were initially low, declined over time. Immunoglobulin M and Immunoglobulin A remained instinct even after repeated testing.

Evaluation of Immune Response

• The horse was given foreign antigens to observe how its immune system would respond, however, it failed to produce any antibodies at all.
• A cell-mediated skin reaction to an intradermal phytolectin injection was affirmative, which suggests the horse indeed had a working adaptive immune system—just one that produced no antibodies.
• Further investigation of its lymphocytes revealed they were responding normally to in vitro stimulation by mitogens, this indicates that the T-cell function of the horse was intact.
• Upon histologic examination of the lymphoid tissues, an absence of germinal centers and plasma cells was observed, which confirmed the diagnosis of agammaglobulinemia, as both these cell types are key players in the production of antibodies.