F₁ cross-breed between susceptible BALB/c and resistant Swiss mice infected with Leishmania major exhibit an intermediate phenotype for lesion sizes and type 1 cytokines but show low level of total IgG antibodies

Our current understanding of the host immune response during leishmaniases largely derives from studies performed in mice due to the intrusive techniques required to study infected human patients. Swiss mice are highly resistant to Leishmania infections in concordance with observed response in humans, while BALB/c mice indicate a high-susceptibility phenotype. Developing a cross-breed between BALB/c and Swiss mice may have important consequences on disease development, immune responses and parasite killing, as yet, response of the cross-breed to Leishmania infection is superficial. The aim of the present study was to determine disease course and immune responses in F₁ cross-breed between BALB/c and Swiss albino mice infected with L. major. Three mice groups were infected intradermally with stationary-phase L. major parasites with parental strains (BALB/c and Swiss albino) as controls. Lesion development was monitored weekly for 8 weeks and monocyte chemotactic protein (MCP-1), macrophage inflammatory protein (MIP-1α), interferon-gamma (IFN-γ) and IgG antibody quantified by enzyme-linked immunosorbent assay. The data were analysed using one-way analysis of variance and Tukey-Kramer test. Results indicated F₁ mice having intermediate lesion sizes, type 1 cytokine levels and footpad parasite loads as compared to the parental strains. However, the F₁ mice had low levels of IgG antibodies and parasite burden in the spleen. (P < 0.05). This study concludes that the F₁ cross-breed between resistant and susceptible mice may be used as a requisite model to study the role of genetics in leishmaniases and perhaps other intracellular parasites.

Immunization with Leishmania vaccine-alum-BCG and montanide ISA 720 adjuvants induces low-grade type 2 cytokines and high levels of IgG2 subclass antibodies in the vervet monkey (Chlorocebus aethiops) model

The availability of hundreds of adjuvants has prompted a need for identifying rational standards for the selection of adjuvant formulation based on sound immunological principles for human vaccines. As cytokines elaborated by activated T cells are required for the regulation of isotype switch during B-cell development, a study of Th2 cytokines and subclass distribution of the antibodies may shed new light on the processes involved in the polarization of the immune responses during vaccination studies. The aim of this study was to identify an appropriate Leishmania vaccine adjuvant based on low Th2 cytokine and high value IgG2 antibody responses. Groups of vervet monkeys were immunized with Leishmania donovani sonicate antigen (Ag) alone or in conjunction with alum-BCG (AlBCG), monophosphoryl lipid A (MPL) or montanide ISA 720 (MISA) as adjuvants. Following three time point intradermal injections on days 0, 28 and 42, IL-4, IL-10 and IgG antibody subclasses were quantified by enzyme-linked immunosorbent assay (ELISA) and data analysed by one-way analysis of variance, Tukey-Kramer test and Spearman's rank correlation analysis. Results indicated relatively higher IL-4 and IL-10 cytokine responses following MPL + Ag as compared to AlBCG + Ag or MISA + Ag immunization. There was a positive significant correlation between IL-4 and IL-10 levels (r = 1.000; P = 0.0167). Significantly higher IgG2 antibody responses were associated with either AlBCG + Ag or MISA + Ag as compared to MPL + Ag immunization (P < 0.05). The study concludes that both AlBCG and MISA may be used in Leishmania vaccine studies that favour low Th2 cytokine and strong IgG2 antibody responses.