A feline homologue of CD1 is defined using a feline-specific monoclonal antibody

The characteristics of a feline homologue of CD1, defined by a murine monoclonal antibody, Fe1.5F4 (IgG1), are described. This antibody precipitated a 49 kDa protein from biotinylated feline thymocyte extract in conjunction with a 14 kDa protein, consistent with beta 2 microglobulin subunit. The tissue distribution of this antigen was restricted to cortical thymocytes and antigen presenting cells of the thymic medulla, epidermis (Langerhans cells), dermis and occasional dendritic cells in the mantle and periarteriolar lymphoid areas of the spleen. Although flow cytometry demonstrated a continuous distribution of antigen expression on thymocytes, antigen density was found to decrease with age, consistent with physiological thymic involution. Thymocytes with high density expression of this antigen were predominantly restricted to cells with dual expression of CD4 and CD8 as defined by feline specific murine monoclonal antibodies Fe1.7B12 (IgG1) and Fe1.10E9 (IgG1) respectively. The tissue distribution of this CD1 homologue indicates that it is a member of the classic thymic CD1 family. This feline homologue of CD1 was distinct from CD1c by virtue of its lack of expression in peripheral blood and splenic mantle zone B cells. An unequivocal distinction could not be made between CD1a and CD1b based on tissue distribution due to species variation in expression of these CD1 molecules. Although the biochemical characteristics of this feline CD1 homologue more closely match with CD1a. The pattern of tissue expression and biochemical characteristics of the feline CD1 antigen appear largely similar to those described for human and other species.