Department of Biosciences, M.D. University, Rohtak - 124001.
Insects causing havoc to human health are difficult to control by insecticides. The recent surge in malaria cases, the spread of multi drug resistant parasites and the emergence of insecticide resistant anopheline mosquitoes has emphasized the need for effective malaria control strategies and bolstered research efforts towards the development of vaccines. Recent studies on anti-arthropod vaccine opens new avenues to disrupt the reproductive physiology of the insects. It is well established that ovarian proteins/insect vitellogens are synthesized by the female fat body (Dhadialla and Raikhel, 1990) and secreted in the haemolymph which are then selectively sequestered to the developing oocyte by receptor mediated endocytosis (Giorgi et al., 1998) and stored in yolk granules (Raikhel and Dhadialla, 1992). Therefore, the antibodies against haemolymph may disrupt the reproductive physiology of the mosquitoes. Here we identified the putative antigens as next rational step towards anti-mosquito and transmission blocking vaccine.
Rabbit antibodies to haemolymph antigens of A. stephensi reduced the fecundity as well as viability in A. stephensi. Total 11 immunogens of mol. Wt. 102.5, 101, 100, 96, 88, 80, 64, 55, 43, 29 and 23 kDa were identified by western blotting. However, ingestion of these antibodies did not show much effect on the engorgement of mosquitoes but delayed the egg laying significantly. Antisera raised against haemolymph proteins was also used to identify cross reactive antigens / epitopes present in other tissues by western blotting as well as by in vivo ELISA. In addition, significant reduction in oocyst development was also observed in A. stephensi mosquitoes that ingested antihaemolymph antibodies along with P. vivax. The expression of almost all polypeptides was reduced in haemolymph and ovary of the immune fed mosquitoes when compared with control. However, there was no significant difference in case of midgut and salivary glands. Seven polypeptides 100, 90, 84, 80, 62, 19 and 12.5 kDa were absent in haemolymph and five 92, 90, 80, 60 and 55 kDa were absent in ovaries. Changes in the polypeptide pattern have been correlated with the fecundity reduction due to immunized blood feeding. The results confirmed the feasibility of targeting mosquito antigens for novel anti-mosquito as well as transmission blocking vaccine development.
