Accelerated influx of dendritic cells into the lymph nodes draining skin sites exposed to attenuated cercariae of Schistosoma mansoni in guinea-pigs.

We compared temporal changes in the cell composition of the skin-draining lymph nodes (SLN) in guinea-pigs exposed percutaneously to normal or attenuated cercariae of Schistosoma mansoni. Different populations were analysed by flow cytometry of double-stained cells by monoclonal antibodies to the major histocompatibility complex class II molecule and lymph node cells of guinea-pigs. Exposure to S. mansoni caused a marked increase in the proportion of B cells and dendritic cells (DC) on day 2, reaching a peak number on day 4. These changes were comparable in both infected and vaccinated animals exposed to normal or attenuated parasites, respectively. Total number of DC, however, showed different kinetics; in infected animals, the number peaked on day 2 and then gradually declined, whereas it reached a higher peak on day 4 in vaccinated animal. Daily injection of bromo-deoxyuridine after exposure to the parasite reduced the total number of DC in the SLN on day 4. A reduction in DC counts in the contralateral side SLN was also evident in vaccinated animals. Our results indicate that a significant number of newly formed DC are recruited to the skin by 4th day of vaccination, followed by increased efflux to the SLN. It is possible that retention of attenuated S. mansoni in the skin may cause accelerated recruitment of newly formed DC from the bone marrow, and facilitate transport and processing of antigens highly expressed on attenuated parasites.