Study of the immune adjuvant effect of chitin microparticles on plasma levels of IgG1 and IgG2a during immunization against Leishmania infection in BALB/c mice

Background: There are reports on the ability of chitin microparticles to modulate the TH1 and TH2 responses, depending on the size and administration route. The purpose of the present study was to investigate the immunoadjuvant effects of the small-sized (less than 40 microns) chitin microparticles (CMP) in vaccination against Leishmania major for preventing leishmaniasis in BALB /c mice by determining IgG1 and IgG2a. Methods: BALB⁄c mice in test and control groups (6 mice per group), during 21 days were immunized subcutaneously three times with soluble Leishmania antigens (SLA) or SLA/CMP. Three weeks after the last immunization, blood sampling was performed and immunoglobulin isotype was determined using ELISA. Then 2 × 105 L. major promastigotes were injected into the base of the tail of the mice. Next, onset and size of the lesions were measured in each group. In the eighth week, blood samples were obtained from the eye for evaluation of IgG1 and IgG2a level and then the mice were sacrificed and their lymph nodes were isolated to determine the parasitic burden using Limiting dilution assay (LDA). Results: The SLA / CMP-immunized mice in compared to the non-immunization group, the onset of the wound were postponed and the parasitic load [(0.41±3.9 Vs.0.82±5.8 Log (Parasites per lymph node)] (P≤0.05) and the extended area of the wound (P≤0.007) were significantly decreased. The results of the serum IgG1 and IgG2a assay showed that immunization by chitin microparticles caused significant decrease in the serum IgG1 level before (P≤0.001) and after (P≤0.014) the challenge but not IgG2a. Conclusion: Co-administration of CMP/SLA cause significant inhibition of IgG1 responses. It seems that CMP could downregulate unbridled TH2 response in Leishmania infection.