Immunomodulatory properties of Mycoplasma pulmonis. III. Lymphocyte stimulation and cytokine production by Mycoplasma pulmonis products.

Experiments are presented that were performed in order to understand the mechanisms causing these effects on the immune system. Mitogenic effects of Mycoplasma membranes on mouse spleen cells were shown using M. capricolum. The observed mitogenic activity is proportional to the amount of membranes used, as measured by protein content. Separation of T and B cells was performed by two techniques, the anti-Thyl.2 plus complement method and the Dynabead technique. Using the former technique, it was shown that removal of T cells markedly reduced effects of stimulation by mycoplasma membranes, but did not abolish it. The separated cells were still stimulated by PHA, indicating that the preparation still contained T cells. Furthermore, removal of T cells preferentially reduced the PHA response over that of mycoplasma membranes, indicating that mycoplasma membranes stimulate both B and T lymphocytes. The Dynabead system was found to be the more efficient separation technique, and by using it we were able to make the following observations. Inactivated Mp, membranes and culture supernatant stimulated B cells, whereas T cells were only slightly stimulated by inactivated Mp and membranes. There was an increase in proliferation when T cells were incubated with adherent cells from peripheral blood. Finally, we showed that spleen cells from infected animals produce more IL-4 and less IFN-gamma than cells from non-infected animals when stimulated with membranes, inactivated Mp, culture supernatant or phytohemagglutinin. Altogether, these results show that lymphocytes from Mycoplasma-infected animals are directly affected and this effect is probably due to superantigen-like molecules from M. pulmonis.