Downmodulation of CD3epsilon expression in CD8alpha+beta- T cells of feline immunodeficiency virus-infected cats.

Feline immunodeficiency virus (FIV) infection in cats is associated with an increase of feline CD (fCD)8alpha+beta- and fCD8alpha+beta low cells in peripheral blood. To investigate these cells in more detail, an anti-fCD3epsilon mAb, termed NZM1, was generated, which recognizes the extracellular epitope of the fCD3epsilon molecule. The anti-fCD3epsilon mAb proved to be more suitable for identifying feline T cells than the anti-fCD5 one, which has been used as a pan-T-cell reagent in cats, because of the presence of fCD5+fCD3epsilon- cells among lymphocytes. Although the fCD8alpha+beta- and fCD8alpha+beta low cells in the FIV-infected cats expressed fCD3epsilon, a subset of fCD8alpha+beta- cells expressed fCD3epsilon antigen at a lower level than the T cells whose phenotype was fCD4+, or fCD8alpha+beta low. The lower expression of fCD3epsilon may be associated with the immune status of fCD8alpha+beta- T cells.