Lysozyme stimulates lymphocyte proliferation in monocyte-depleted mixed lymphocyte cultures.

Human LZM was found to enhance 3H-thy uptake and lymphoblast transformation in monocyte-depleted MLC. The effect was maximal (up to sixfold increase) in "low level" (less than 10,000 cpm) MLC. Maximal MLC enhancement was obtained with 250 micrograms/ml LZM; higher LZM concentrations appeared to be inhibitory. LZM enhancement of MLC could not be demonstrated in the presence of monocytes. LZM did not enhance lymphocyte responses to SKSD. Several observations support the possibility that LZM enhancement of MLC is due to LZM augmentation of stimulator cell antigenicity. LZM pretreatment of stimulator but not responder lymphocytes enhanced MLC. This enhancement was blocked by the LZM inhibitor tri-GlcNAc. LZM enhancement of MLC was maximum when the antigenic stimulus was minimized by either reducing the number of stimulator cells or utilizing DRw-matched donors in MLC. These data suggest that (1) LZM may enhance lymphocyte proliferative responses to allogeneic stimuli by altering stimulator cells' antigenicity and (2) monocyte-macrophage enhancement of lymphocyte proliferation in MLC may be partially mediated by LZM. (J Lab Clin Med 99:370, 1982.)