Nonspecific Cytotoxic Cells in Fish: Antigenic Cross-Reactivity of a Function Associated Molecule with the Intermediate Filament Vimentin

Nonspecific cytotoxic cells (NCC) in fish may lyse tumor cells and protozoan parasites in a similar fashion as their mammalian NK counterparts. Previous studies have shown that recognition and binding by NCC may be mediated by a receptor. In the present study the putative receptor of function-associated molecule (FAM) on NCC was shown to contain antigenic cross-reactivity with the mammalian intermediate filament vimentin. This was accomplished by comparing the specificity of anti-FAM monoclonal antibody 5C6 with commercially available anti-vimentin mabs V9 and 13.2 and with a polyclonal anti-vimentin antiserum. Tissue distribution studies indicated that tile anti-vimentin antibodies bound to significantly fewer (<50%) anterior kidney, spleen, kidney, and brain cells than mab 5C6. These mabs, however. produced inhibition of NCC lysis of IM-9 target cells. Conditions of mab incubation (with NCC) which were previously shown to modulate NCC cytotoxicity by 5C6 also produced large increases in NCC lysis of IM-9 targets in the presence of mabs V9 and 13.2. The determinant(s) recognized by these antibodies is present on the cell membrane. Microscopic examination of nonpermeabilized or acetone-treated and antibody-stained cells demonstrated that acetone permeabilization produced a 28-32% increase in staining (due to intracellular binding) compared to the staining of viable cells. Biochemical analysis of the cross-reactive antigens was done using analytical 2D SDS-PAGE and Western blot experiments. Mab 5C6 detected a 32- to 35-kDa protein (pl 6.3 6,5) in NCC extracts. Antivimentin mab 13.2 recognized a 57-kDa vimentin protein which had a relatively broad pl range (pH 6.3-6.7). Mab 13.2 also cross-reacted (in the same Western blot) with the NCC receptor protein (pl = pH 6.3-6.5). These data indicate that the FAM on NCC/NK cells contain vimentin-like antigenic determinants which may function in target cell binding.