Inhibitory effect of circulating egg antigens on Schistosoma japonicum egg-induced granuloma formation

Schistosoma japonicum produces an enormous quantity of eggs during infection. This study was conducted to examine the effect of egg-derived antigens on the development of granuloma formation around S. japonicum eggs in the livers of mice. When soluble egg antigen (SEA) (75 micrograms/mouse/day) was injected 3-4 times via a vein into mice implanted with laid eggs, the magnitude of tissue lesion was drastically inhibited when assessed at maximal occurrence (14 days after implantation of eggs), whereas adult worm antigen (AWA), rabbit hyperimmune serum against SEA, or bovine serum albumin (BSA) did not show any effect on either the cellularity or the magnitude. In contrast to intravenous injection, there was no effect from subcutaneous injections of SEA. When serum taken from heavily infected mice or rabbit was transferred, there was a considerable extent of inhibition. In addition, an immune complex fraction of infected rabbit serum was found to have a stronger inhibitory effect than the supernatant fraction. This study indicates that the amount of egg-derived circulating antigens has a crucial effect on the development of schistosome granuloma formation.