RESUMEN
The mouse major histocompatibility complex (MHC) class I sequence was detected in all the 8-week-old Schistosoma japonicum recovered from BALB/c (H-2d) and C57BL/6 (H-2b) mice by in situ polymerase chain reaction (in situ PCR). The signals of the mouse class I MHC sequence were observed in the nuclei of the mesenchymal and reproductive cells of 8-week-old S. japonicum. Furthermore, the class I MHC sequence was detected in each DNA extracted from S. japonicum cercariae maintained in BALB/c and C57BL/6 mice by nested PCR. To prove both horizontal and vertical transmission of this sequence in schistosomes, we have used cercariae obtained from parasites maintained in BALB/c mice to infect C57BL/6 and BALB/c mice, and vice versa. The MHC sequences from adult worms were compared to the cercarial MHC and host MHC sequences. Nucleotide sequence comparisons between adult worm DNA, host (H-2d and H-2b mice) DNA and cercarial DNA used for the infection suggested that the sequence of mouse class I MHC was incorporated into schistosome adults and inherited throughout their life-cycle.