Cell-mediated immunity during natural measles infection.

Natural measles causes prolonged depression of cell-mediated immunity yet little is known as to how the infection influences lymphocyte function. Therefore, we studied the properties and function of lymphocytes during and after measles. The number and proportion of circulating thymus-derived lymphocytes was low during the acute stage of measles, and at this time 37% of these cells showed positive immunofluorescent staining for measles virus after stimulation with phytohemagglutinin. 7% of B cells were shown to contain virus but their numbers did not alter during the infection. Acute-phase lymphocytes, when stimulated, yielded infective virus and half were killed on incubation with autologous serum and complement. In acute measles the increase in [(3)H]-thymidine uptake of lymphocytes when stimulated with an optimal dose of PHA was normal in media with 10% fetal calf serum and low in media containing 10% autologous serum: the mean values were 56.8+/-34.1 and 23.7+/-25.9 cpm x 10(3) per 10(6) lymphocytes, respectively. Stimulation of acute-phase lymphocytes by Candida antigen was also low in media containing autologous serum averaging 1.2 x 10(3) cpm per 10(6) lymphocytes. On recovery 4-6 wk later this rose significantly to 18.9+/-19.8. The mean migration index of leukocytes to heat-killed candida cells in acute measles was 0.84+/-SD 0.08, and this fell significantly to 0.75+/-SD 0.08 4 wk later. Thus, depletion of T cells, an inhibitor of lymphocyte proliferation in the serum and a possible defect in antigen processing, interacts to depress cell-mediated immunity in measles.