T-cell-rich, large B-cell lymphoma in the brain of a horse.

This research article describes a case of a type of lymphoma known as T-cell-rich, large B-cell lymphoma (TCRLBCL) in the brain of a male Quarter Horse. The paper discusses the clinical signs observed, the findings from the neuropathology, immunohistochemistry, and receptor rearrangement analysis of the horse.

Clinical Presentation and Necropsy

The report details the clinical signs observed in the horse, which included acute anorexia, tremors, head pressing, falling, blindness, incoordination, and seizures. Due to the severity of these symptoms, the horse was euthanized. Upon autopsy, a firm, smooth, pale-yellow mass was found expanding both lateral ventricles and the adjacent subcortical white matter of the brain.

Neuropathology and Immunohistochemistry Results

• The mass histologically consisted of a densely cellular tumor composed of large, CD79+ neoplastic B-lymphocytes (a marker for B cells) mixed with sheets of CD3+ reactive T-lymphocytes (a marker for T cells).
• Also present were Iba1+ histiocytes (immune cells that regulate brain development and immune response), MUM1+ plasma cells (cells that produce antibodies), and rare eosinophils (cells involved in the immune response) and these were all supported by a fine fibrovascular stroma (a connective tissue network).

PCR for Antigen Receptor Rearrangement Analysis

• The researchers also conducted PARR (PCR for Antigen Receptor Rearrangement) analysis, which is a technique to study the arrangement of genes in immune cells.
• In this study, it revealed a clonal reaction in the immunoglobulin gene (indicating a proliferative response by the B-lymphocytes) and a polyclonal reaction for the T-lymphocyte receptor gene (indicating a reactive proliferation of the T-lymphocytes). Both of these findings are consistent with a neoplastic B-lymphocyte (cancer) and reactive T-lymphocyte proliferation.

Diagnosis

Through histological examination, the diagnosis of T-cell-rich, large B-cell lymphoma (TCRLBCL) was suspected. This is a common form of lymphoma in horses. It is characterized by a considerable amount of T-cells alongside large B-cells which are the actual malignantly transformed cells. The diagnosis was confirmed via immunohistochemistry (IHC) – staining the cells to better see their identity and structure, and PARR analysis – to better understand the genetic makeup of the cells, both of which supported the histological diagnosis.