Common variable immunodeficiency in a horse.

The study investigates common variable immunodeficiency (CVID) in a 12-year-old Quarter Horse mare suffering from chronic respiratory and hepatobiliary diseases. The horse, which didn’t respond to standard medical treatments, had near non-existent concentrations of important immune system proteins. The horse’s immune responses to vaccines and stimulants were also impaired, suggesting a diagnosis of CVID.

Study Process

• The researchers began their investigation into the mare’s persistent health issues by measuring the concentrations of key immunoglobulins—proteins critical to the immune response—in her serum. Using a process known as radial immunodiffusion, they detected nearly non-existent concentrations of IgG, IgG(T), IgM, and IgA.
• Naturally high concentrations of these immunoglobulins are crucial for maintaining a healthy immune response. Their near absence meant that the mare’s immune response was likely compromised, disrupting her ability to effectively fight off disease.
• To corroborate this, serum protein electrophoresis—a method for separating proteins according to their size and electrical charge—was used. The result confirmed agammaglobulinemia (a lack of immunoglobulins in the blood), seen by the absence of the expected peak within the gamma region, a place in the electrophoretic pattern where immunoglobulin G (IgG) usually is abundant.

Vaccination Test

• Further tests were conducted by vaccinating the mare with tetanus toxoid to determine if her immune system was capable of producing specific immunoglobulins in response to a vaccine. Unfortunately, the mare’s immune system did not respond with any significant antibody production, indicating a dysfunctional immune response.

Flow Cytometric Analysis

• Flow cytometric analysis was used to further ascertain the health of the mare’s immune system. This is a technique used to measure physical and chemical characteristics of a population of cells or particles. In this case, it revealed the absence of B cells in the horse’s blood.
• B cells are lymphocytes that play a crucial role in humoral immunity (part of the immune system that functions to produce antibodies). They initiate antibody production by recognizing antigens and maturing into plasma cells. Their absence in the blood points towards a major compromise in the horse’s immune system.
• This finding was further confirmed through immunohistochemical analysis of tissue sections from the bone marrow and spleen, which also revealed an absence of B lymphocytes. Only occasional B cells were found in peripheral lymph nodes.

Blood Lymphocyte Proliferation Assays

• Additional tests, called blood lymphocyte proliferation assays, showed weak responses to pokeweed mitogen (a plant protein that stimulates cellular proliferation) and absolutely no response to stimulation with lipopolysaccharide (a much more potent immunostimulator).

Conclusion

• across a variety of tests, the horse showed a consistent inability to generate a normal immune response, suggesting a diagnosis of common variable immunodeficiency (CVID), a disorder that impacts the immune system and results in the decreased production of immunoglobulins.
• CVID is a rare disorder in horses and is usually diagnosed in young animals. However, considering the age and sex of this horse, and the definitive results of the immunologic tests, a diagnosis of CVID was made.