Agammaglobulinemia in a horse

Area of Science:

• Veterinary Immunology
• Equine Medicine
• Immunodeficiency Disorders

Background:

• Persistent fever, multifocal bacterial infections, and neutropenia in an 18-month-old Standardbred horse suggested an underlying immunologic deficiency.
• Initial clinical signs included recurrent infections and an abnormal white blood cell count with immature neutrophils.

Observation:

• Serum protein electrophoresis showed a severely depressed gamma-globulin fraction (0.2 g/100 ml).
• Immunologic testing and lymphoid tissue histology confirmed agammaglobulinemia, characterized by extremely low or undetectable levels of IgG, IgG(T), IgM, and IgA.
• The horse exhibited an inability to mount an antibody response to foreign antigens.

Findings:

• Cell-mediated immunity was intact, indicated by a positive skin reaction to phytohemagglutinin.
• Lymphocytes demonstrated normal in vitro responses to mitogenic stimulation.
• Histological examination of lymphoid tissues revealed a lack of germinal centers and plasma cells, consistent with a B-cell defect.

Implications:

• This case highlights agammaglobulinemia as a cause of severe combined immunodeficiency in horses.
• Understanding this condition is crucial for accurate diagnosis and management of recurrent infections in equine patients.
• The findings underscore the importance of immunoglobulin levels in diagnosing and characterizing B-cell deficiencies in veterinary medicine.