Common variable immunodeficiency is characterized by what immunologic defect?

• A. Low immunoglobulin levels with impaired antibody responses despite normal B and T cell numbers.
• B. Absent B cells
• C. Hyper-IgM syndrome
• D. Overproduction of IgE

Answer: (A)

Humoral immunodeficiency with low antibody production despite normal lymphocyte numbers. In common variable immunodeficiency (CVID), B cells are present, but their ability to mature into antibody-secreting plasma cells is impaired, leading to decreased immunoglobulin levels (often IgG with low IgA, sometimes IgM) and a poor antibody response to vaccines and infections. This pattern—hypogammaglobulinemia with ineffective antibody production despite normal B and T cell counts—defines CVID.

This distinguishes CVID from conditions like agammaglobulinemia, where B cells are absent; from hyper-IgM syndrome, where class-switching is defective and IgM is high with low other isotypes; and from disorders with isolated IgE abnormalities. Clinically, CVID presents with recurrent sinopulmonary infections and may include autoimmunity or lymphoproliferation, and treatment often involves immunoglobulin replacement therapy to reduce infection risk.