Histological changes in the spleen of BALB/C mice caused by excretory-secretory protein(s) of Setaria digitata (Von Linstow).

The hatching associated materials generally called the excretory-secretory material (ES) released from the filarial parasite S. digitata along with the microfilariae (mf) under in vitro conditions showed immunosuppression. However the protein from lysate of embryo zone, from which ES materials were released along with the mf showed immunopotentiation in BALB/C mice. The histological analysis of spleen of immunized BALB/C mice showed changes confirming the in vitro findings. The main changes observed in the suppressed spleen were decrease in size and number of lymph follicles and increase in number of reticuloendothelial (RE) cells and cosinophil cells, whereas the main change in the potentiated spleen was an increase in the number of lymph follicles as compared to control spleen. These results clearly indicate that there are two types of ES materials in S. digitata, the native material present in the mature embryo causes immunopotentiation, and the materials released during the hatching process into the hostile environment along with mf causes immunosuppression. The difference in the biological effect between the materials released by lysis and hatching of the embryo opens up fresh understanding about the survival strategies of filarial parasites.