MECHANISMS INVOLVED IN THE LOSS OF ANTIBODY-MEDIATED ADHERENCE OF MACROPHAGES TO LUNG-STAGE SCHISTOSOMULA OF SCHISTOSOMA-MANSONI IN-VITRO

Sera from rabbits vaccinated with irradiated cercariae mediated cell ( P388D1 or mouse peritoneal macrophage) adherence to lung-stage schisto somula (LS) but such antibody-mediated cell adherence was short-lived in contrast to cell adherence to mechanically transformed schistosomul a (MS). Thus LS lost 50% of their adherent cells within 3-6 h in cultu re and up to 90% by 24 h, whereas adherence to MS was undiminished dur ing this time. Rapid loss of adherent cells was unique to schistosomul a that had developed to the lung stage because schistosomula recovered from the skin up to 3 days postinfection did not exhibit the rapid ce ll loss shown by 3-day LS. To determine whether cell loss was caused b y loss of surface antigenicity during culture LS were cultured on thei r own for up to 24 h and at various intervals samples of schistosomula were tested for antigenicity by addition of immune serum and cells. L evels of adherence to both MS and 1,S were maintained throughout the i ncubation period. When antibody-opsonized schistosomula were washed an d indicator cells added at progressive intervals, persistence of adher ence was again demonstrated, showing that antibody binding to LS had n ot promoted surface antigen loss or degradation of bound antibody. It was then shown, by adding fresh macrophages to cultures up to 24 h old that LS which had lost their adherent cells nevertheless retained bou nd antibody, and comparison of adherence of 'used' and 'fresh' cells t o MS and LS showed that the cytoadherence properties of macrophages we re not significantly reduced during their culture with LS from which c ells had been lost. Cell loss was shown to be dependent upon protein s ynthesis by LS since cell loss was significantly reduced when the schi stosomula were pre-incubated in puromycin or actinomycin D. Transient cell adherence to LS may comprise an important immune evasion stratage m by schistosomula.