Helper T cell and antibody responses to infection of CBA mice with Babesiamicroti

Helper T cell cytokine and antibody responses were investigated in mice aft er infection with Babesia microti (King strain). Infection of CBA mice with 10(6) parasitized erythrocytes resulted in the development of a transitory high parasitaemia which peaked 14 days post infection (DPI), and was resol ved at 24 DPI. Th1 responses were activated predominately during the acute phase (6-18 DPI) whereas Th2 responses predominated during the recovery pha se (14-28 DPI) as detected by the reverse transcriptase polymerase chain re action. Increased expression of Th1 cytokines was first detected at 6 DPI ( IL-2) and 8 DPI (IFN-gamma) and their peak levels were reached at 12 DPI. A fter the peak levels were reached, they progressively declined and fell to baseline levels (22 DPI). Increased expression of Th2 cytokines (IL-4 and I L-10) first appeared at 14 DPI, peaked at 20 DPI and Th2 cytokine levels we re elevated till the end of the study (28 DPI). Levels of serum IFN-gamma d etected by a sandwich ELISA correlated well with IFN-gamma gene expression and were detectable at 8-18 DPI. IgM against B. microti was first detected in serum by ELISA at 4 DPI, and peaked at 10 DPI. The levels of IgM subsequ ently declined but remained positive at low titre till the end of study. Ig G against B. microti was first detected at 8 DPI and peak levels were reach ed at 24 DPI and remained at that level until the end of study. The results of the present study show that Th1 cytokines predominated in the early inf lammatory response and might be involved in control of levels of acute para sitaemia whereas the Th2-associated responses, including expression of IL-4 and IL-10 and the production of parasite-specific IgG, might be the functi onal means for the reduction and clearance of the parasite from the body. I t was concluded that an effective vaccine against Babesia spp. should be de signed to induce Th1 responses to maintain the parasitaemia at unfulminatin g levels and also maintain Th2 responses to clear the parasite from the bod y.