CD40LG and common variable immunodeficiency: Consistent with this, one 13-year-old gelding in this study with mucocutaneous T-cell and histiocyte-rich B-cell lymphoma was diagnosed with common variable immunodeficiency (CVID) associated with multiple and recurrent infections (salmonella enteritis, pyelonephritis, pneumonia, intramuscular abscess, and fungal keratitis) and impaired antibody production with low serum IgM (<33 mg/dL; reference median 100 mg/dL + 50 mg/dL CI) and IgG (855 mg/dL; reference median 1,760 + 603 mg/dL CI) values.