IMMUNOSUPPRESSIVE ACTIVITY OF BOVINE SEMINAL RIBONUCLEASE AND ITS MODE OF ACTION

Two preparations of dimeric BS RNase - native and recombinant proteins caused identical immunosuppressive effects on MLC-stimulated human ly mphocytes. The monomers of RNase A and BS RNase were ten times less ac tive. The inhibitory effect on MLC-stimmulation was followed by 90 % i nhibition of cell-mediated lympholysis (CML) caused by BS RNase (10 mu g/ml). This effect indicated that BS RNase suppressed the recognition phase of the cytotoxic reaction, resulting in inhibition of generatio n of cytotoxic effector cells. BS RNase exerted a similar effect on ge neration of cytotoxic LAK cells. Cytotoxic activity of LAK cells or CT Ls against K562 target cells was abrogated only when BS RNase was adde d at the beginning of the Sensitizing phase, but the cytotoxicity of e ffector cells in the destruction phase eras not influenced. The effect of RNase A on the generation of cytotoxic cells was much less pronoun ced. To get more information about the site of action, the effect of B S RNase on early lymphocyte stimulation by PHA was investigated by usi ng fluorescein cell probes. BS RNase (100 mu g/ml) prevented a shift i n fluorescein emission occurring within one hour of activation using f luorescein diacetate as a marker for changes in the cytoplasmic matrix . On the contrary, it did not block the shift in fluorescence emission when tested with diphenylhexatrien as a marker for changes in membran e fluidity. Furthermore the effect of BS RNase on expression of membra ne antigens expressed on activated human lymphocytes was estimated. BS RNase significantly inhibited the expression of CD25, CD38 and CD71 a ntigens on PHA-, Con A- and MLC-stimulated human T and B lymphocytes. No substantial change in expression of these antigens was observed on IL-2-stimulated cells, bur DNA synthesis was totally abrogated. These results indicate that the mode of action of BS RNase on activated T an d B lymphocytes is based mainly on the suppressed expression of recept ors for interleukin-2-alpha-chain and transferrin.