Barbara J. Winslow

Feline Immunodeficiency Virus Infection Is Characterized by B7+CTLA4+ T Cell Apoptosis

The B7.1 and B7.2 costimulatory molecules on antigen-presenting cells provide second signals for regulating T cell immune responses via CD28 and cytotoxic T lymphocyte antigen 4 (CTLA4) on T cells. CD28 signals cell proliferation, whereas CTLA4 signals for anergy or apoptosis, terminating the immune response. Because T cell apoptosis and immunodeficiency is a characteristic of feline immunodeficiency virus (FIV)-infected cats, it is possible that negative T cell signaling via B7 and CTLA4 may be favored in these cats. Flow cytometry revealed high percentages of CD8+ and CD4+ cells expressing B7.1, B7.2, and CTLA4 in lymph nodes of FIV-positive cats and a large fraction of CTLA4+ T cells coexpressing B7.1 and B7.2. Three-color analysis with anti-B7.1, anti-B7.2, or anti-CTLA4 and TUNEL (terminal deoxynucleotidyl transferase nick-end-labeling) analysis revealed that apoptosis was a characteristic of B7.1+ B7.2+ CTLA4+ T cells. These data support the hypothesis that lymph node apoptosis and immune deterioration in FIV-infected cats results from chronic B7.1- and/or B7.2-CTLA4-mediated T-T interactions.

Sequence analyses of feline B7 costimulatory molecules.

Using RT-PCR amplifications with mRNA from mitogen-stimulated feline peripheral blood mononuclear cells, cDNA of feline B7-1 (CD80) and B7-2 (CD86) were cloned. The cDNA were sequenced and putative translated protein sequences compared with known counterpart sequences. Hydrophilicity patterns of the feline CD80 and CD86 which were only 26.8% identical at the amino acid sequence were very distinct from each other, but similar to the putative human CD80 and CD86 proteins, respectively. The feline CD80 gene encoded a protein of 292 amino acids and the CD86 gene encoded a protein of 329 amino acids. Amino-terminal signal sequences, extracellular Ig V- and Ig C-like domains, transmembrane domains, and carboxyl cytoplasmic domains were identified in both molecules. Although the most conserved domain among the CD80 sequences was the Ig C-like domain, the most conserved domain among the CD86 sequences was the Ig V-like domain. Among the known sequences, the bovine CD80 and the porcine CD86 sequences available for comparisons were identified as most closely related to the feline CD80 (63.3%) and CD86 (67.5%), respectively. The mouse molecules were the least identical (43.6 and 43.6%, respectively) with the feline CD80 and CD86 proteins. The human CD80 and CD86 molecules were 56.3 and 57.0% identical with the feline molecules.