Immunohistochemical characterization of mononuclear cells and MHC II expression in the brain of horses with experimental chronic Trypanosoma evansi infection.

This research studied the immune response mechanisms in horses experimentally infected by Trypanosoma evansi by evaluating mononuclear cells and major histocompatibility complex II (MHC II) expression in their brains. The findings revealed widespread non-suppurative encephalomyelitis and meningomyelitis in the infected horses, with lesions severity varying across the nervous system.

Research Methodology

• The researchers employed histochemical and immunohistochemical study techniques to examine the effects of deliberate infection by Trypanosoma evansi — a parasite — on the horses’ immune response mechanisms.
• They used special stains (HE histochemical stain) and methods (the avidin biotin peroxidase method) for this purpose.
• Anti-major histocompatibility complex II antibodies were used to establish the presence and immunoreactivity of immune cells.
• The phenotype of the infiltrated cells was examined using anti-CD3 antibody for T lymphocytes, anti-BLA 36 antibodies for B lymphocytes, and an antibody against the myeloid/histiocytes antigen (clone Mac387) for marking macrophages.

Key Findings

• In the central nervous system (CNS) of infected horses, the researchers uncovered widespread, non-suppurative (not producing pus) encephalomyelitis (inflammation of the brain and spinal cord) and meningomyelitis (inflammation of the meninges, the protective membranes of the CNS).
• The inflamed areas, or lesions, differed in their severity across the nervous system, indicating an irregular distribution of inflammatory changes in the blood vessels.
• The team observed that lymphoid perivascular cuffs (swellings around a vessel) and meningeal infiltrations were mainly composed of T and B cells, two types of lymphocytes.
• Interestingly, the parasite Trypanosoma evansi wasn’t detected in the tissue samples of these horses, despite the animals being intentionally infected for the purposes of the study.