Generation of CD8+ suppressor T cells by protoscoleces of Echinococcus multilocularis in vitro.

Addition of protoscoleces (PSC) of Echinococcus multiocularis suppressed proliferative responses in spleen cells stimulated with concanavalin A (Con A) on day 3 of culture. The suppression was not observed in the spleen cell population depleted of CD8+ cells but observed in the population depleted of CD4+ cells, suggesting the involvement of the CD8+ T cells in the apparent suppression. Indeed, flow cytometry analysis revealed that the proportion of CD8+ cells markedly increased in the Con A cultures containing PSC. Furthermore, when spleen cells were co-cultured with PSC alone, marked increase in the proportion of CD8+ cells as well as B220+ cells was observed. Addition of these increasing CD8+ cells suppressed the proliferative responses of fresh spleen cells stimulated with Con A. These findings suggest that the low responsiveness of spleen cells to Con A on day 3 of culture in the presence of PSC is attributable to an active suppressor mechanism including CD8+ T-suppressor cells generated by stimulation with PSC.

Interleukin-1-dependent mitogenic responses induced by protoscoleces of Echinococcus multilocularis in murine lymphocytes.

Mitogenic effects of protoscoleces (PSCs) of Echinococcus multilocularis on murine lymphocytes were studied. Spleen cells from normal BALB/c mice showed significant proliferative responses when cocultured with PSCs. Proliferative responses were observed in both the T and B cell populations. The PSCs also stimulated cells of the macrophage/monocyte lineage to secrete interleukin-1 (IL-1). Depletion of plastic- and Sephadex G-10-adherent cells from the spleen cell population significantly reduced the proliferative responses to PSCs and the low responsiveness was restored by addition of plastic-adherent cells to these cultures. Furthermore, addition of anti-IL-1 serum to the spleen cell cultures stimulated with PSCs completely suppressed the proliferative responses. These findings demonstrate that the mitogenic effect of PSC on lymphocytes depends on IL-1 secreted by cells of macrophage/monocyte lineage.

Suppression of T-cell proliferation by CD8+ T cells induced in the presence of protoscolices of Echinococcus multilocularis in vitro.

Immunoregulatory influences of protoscolices (PSC) of Echinococcus multilocularis on murine T-lymphocyte functions have been examined in an in vitro system. Proliferative responses of spleen cells stimulated with concanavalin A (ConA) or anti-CD3 monoclonal antibodies were depressed by the addition of PSC. In the presence of PSC, both interleukin-2 (IL-2) production and IL-2 receptor (IL-2R) expression by lymphocytes stimulated with ConA were significantly reduced. However, exogenous IL-2 reconstituted both the ConA-stimulated proliferative responses and IL-2R expression. These findings suggest that PSC of E. multilocularis can suppress lymphoid cell responses via influences on IL-2 production. Indeed, addition of CD(8+)-enriched cells from cultures stimulated with ConA plus PSC to fresh spleen cells showed marked suppression of the ConA responses. IL-2 production as well as IL-2R expression on the spleen cells so treated were suppressed. These findings reveal a suppressive immunologic function induced by E. multilocularis PSC that involves inhibition of IL-2 production and reduction of IL-2R expression. The PSC-induced CD8+ cells appear to play a key role in the suppressive regulation of host immune responses against E. multilocularis.

Longitudinal study on Schistosoma japonicum infections in the Philippines. 3. Incidence and environmental modification at Dagami, Leyte.

The yearly change of incidence of schistosomiasis japonica was observed among 1800 children enrolled in 9 schools situated within a 5 km radius around Dagami Poblacion, Leyte, Philippines from School Year (SY) 1974/75 to 1979/80. The purpose of this observation was to know the effect of environmental modification undertaken in about 50 ha of snail-infested and abandoned rice field which is the most depressed and central portion of this project area. Children were examined by egg detection from stool and by circumoval precipitin test. Coverage of examination among the school population ranged from 40 to 80% yearly and the ratio of re-examination after about 1 year was from 30 to 60%. The annual incidence in the different schools differed greatly from 12.15 to 42.86% in contrast to the annual prevalence which differed only slightly. There was corresponding increase of incidence with age from 18.6% at age 7 to 33.9% at age 12 while no significant difference was observed between sexes. The overall annual incidence rates for 9 schools during the 5-year follow-up period (SY 1975/76 to 1979/80) were 22.2, 24.2, 26.9, 9.6 and 28.4%, respectively. Those of Dagami Central II, the nearest school to the reclaimed site, were 15.7, 18.2, 19.3, 5.2 and 11.6%, respectively, for the same period. Obviously, the incidence was increasing while the reclamation was going on except in SY 1978/79. Analysis of the sudden drop of incidence in that year in all the 9 schools showed that it was not due to the effect of reclamation, but was most likely due to scanty rainfall in the previous year (1977). These observations indicated that small scale environmental modification had doubtful effect on outlying endemic areas in reducing the danger of Schistosoma infection but may have a little effect on the immediate surroundings as shown by a lesser elevation of incidence after the abrupt decrease at the nearest school as compared to those of schools located farther from the reclamation area.