Abstract

A previous infection of C3H mice with viable Mycoplasma pulmonis organisms protected them from arthritis induced by intravenous inoculation of these organisms, whether or not their initial arthritis had resolved at the time of challenge. Although spleen cells obtained from such animals conferred resistance to acute arthritis in syngeneic recipient mice, convalescent-phase serum was much more effective in this respect. In addition, the transfer of 'immune' spleen cells to M. pulmonis-infected mice treated with cyclophosphamide did not prevent them from dying, whereas the transfer of convalescent-phase serum to such animals reduced the incidence of mortality. Since M. pulmonis organisms are rapidly inactivated in mice treated with convalescent-phase serum it is suggested that the transferred serum may act by promoting phagocytosis of the mycoplasmas. Although the reason for some mice developing a prolonged arthritis is not clear, the results show that humoral immune mechanisms are more important than cell-mediated ones in preventing acute arthritis and that the humoral mechanisms are of greater importance than the cell-mediated in resistance to and recovery from a generalized mycoplasma infection.