EFFECT OF LEVAMISOLE ON THE IMMUNE-RESPONSE OF PATIENTS WITH SCHISTOSOMIASIS AFTER TREATMENT WITH PRAZIQUANTEL

Successful therapy with praziquantel in schistosomiasis is dependent o n a normal host immune system, i.e. the recognition of parasite antige n, to be effective in eradicating the parasite. Levamisole, a nonspeci fic immunomodulator, has been hypothesised to normalise deficient cell -mediated immunity. The aim of this study was to investigate the effec t of levamisole on the immune response seen after presumed curative do ses of praziquantel. After ethical approval, 29 male volunteers infect ed with Schistosoma haematobium were recruited and randomised to recei ve orally either (a) levamisole 5 mg/kg for 2 consecutive days, plus p raziquantel 40 mg/kg as a single dose, (b) levamisole 5 mg/kg for 2 da ys, or (c) praziquantel 40 mg/kg as a single dose. Blood samples were collected on day 0 and again 3 months later for differential counts an d specific IgG and IgE to whole-worm-antigen, as well as for the detec tion of eosinophil cationic protein (ECP). Levamisole treatment alone resulted in a significant drop in circulating eosinophil counts, i.e. a median (95% confidence interval) drop of 6.0 (1;7)%. Eosinophil coun ts did not change significantly after praziquantel therapy alone. ECP values were significantly reduced with levamisole alone and praziquant el alone, i.e. respective median (95% confidence interval) drops of 33 .58 (18.94; 55.9) and 16.54 (3.6; 33.5) mu g/L (p < 0.05). The group r eceiving combination therapy demonstrated significant increases in spe cific IgG values (p = 0.02) with no decline in ECP levels and eosinoph il counts compared with baseline values. Levamisole alone had no effec t on egg counts. In conclusion levamisole inhibited circulating eosino phils and eosinophil activation when given alone, but caused immune st imulation when combined with praziquantel. The exact mechanism of acti on still needs to be determined.