Introduction: Giardia lamblia, a protozoan intestinal parasite is able to evade or suppress defense mechanisms, such as innate response. Antigen presenting cells (APC) like dendritic cells may orchestrate an immune response and support a more effective adaptive defense. Conjugated linoleic acid (CLA), a dietary lipid, has shown biological activity on APC. The aim was to evaluate the effect of CLA in intestinal innate response measuring the frequency of mucosal APC populations in Giardia lamblia murine infection.Method: The giardiasis infection model was established in C3H/HeN mice (n=32), and parasite load was followed at 0, 2, 6 and 8 days post infection (dpi). APC obtained from small intestine by enzymatic digestion were assessed by flow cytometry. Oral supplementation with CLA (50:50 of cis-9, trans-11-CLA and trans-10, cis-12-CLA isomers) and placebo control begun three days before infection and continued during first week post infection.Results: Infection kinetics showed a peak of trophozoites at 6 dpi in acute phase. Parasite load was lower in CLA group in comparison with control infected group (p<0.05). Conjugated linoleic acid stimulates innate immune response, percentage of intestinal CD11chiMHC-IIhi increases after 2 dpi, meanwhile CD11chiMHC-IIhiCD103+ APC was higher after three days of CLA supplementation than control (p<0.05). Also, the CD11c+ F4/80+ population shown a percentage increases after 6 and 8 dpi by the effect of treatment and time of infection (p<0.05).Conclusion: In conclusion CLA increased percentages of small intestine APC phenotypes CD11chiMHCIIhi, CD11chiMHCIIhiCD103+ and CD11c+ F4/80+, and reduced G. lamblia parasitic load. Further studies are needed to elucidate potential mechanisms involved in CLA immunomodulatory effect and its contribution in adaptive immune response. 

Hybrid Th1/Tfh cells (IFN-γ+IL-21+CXCR5+) predominate in response to persistent infections. However, it is not clear if the function of these cells is plastic and might be modulated. In infection with Plasmodium spp, an IFN-γ+ T helper-1 (Th1) response controls initial parasitemia, while antibody and IL-21+CXCR5+ T follicular helper (Tfh) function effect final clearance. Supporting plasticity, we found that CD4-intrinsic Bcl6, Blimp-1 and STAT3 all regulate T-bet expression, which controls IFN-γ expression. While Bcl6 and Blimp-1 regulate the level of CXCR5, only T-bet, IL-27Rα and STAT3 strongly affected the cytokine bias of the Th1/Tfh phenotype. Infected mice with STAT3-deficient T cells produced less antibody, and more Th1-like IFN-γ+IL-21−CXCR5lo T cells, significantly increasing protection from re-infection. Conversely, reduced Th1 bias in re-infected T-bet KO was reflected in prolonged secondary parasitemia. Signs of pathology were somewhat prolonged in Th1-biased animals supporting an evolutionary tradeoff between control of parasite and tissue damage. In summary, each feature of hybrid Th1/Tfh population in Plasmodium infection is uniquely regulated and the cytokine bias of memory T cells can be modified to enhance the effectiveness of the response.

Germinal center (GC) formation in P. chabaudi rodent malaria is delayed for three weeks, which can prolong the infection. T follicular helper (Tfh) cells express CXCR5 for homing to the B cell area, and IL-21 which promotes antibody production. T helper type 1 (Th1) cells express CXCR3 and IFN-γ to promote phagocytosis. Previous data suggests that Th1 responses control peak parasitemia while systemic Th1 cytokines inhibit GC formation. In P. chabaudi, majority of CD4+ effector T cells (Teff) express markers of both Th1 and Tfh (e.g., CXCR5, CXCR3, Th1/Tfh hybrid), including IFN-γ and IL-21. The contribution of Th1/Tfh hybrid T cells in protection and antibody production remains unclear. We tested the impact of Il21+Tfh-like, Ifng+Th1-like, and Ifng+Il21+Th1/Tfh in protection by transferring these subsets from infected triple cytokine reporters (Il21-rfp Il4-gfp Ifng-Thy1.1) into TCR KO mice that are then infected. We are currently assessing changes in parasitemia and pathology. We found that Th1/Tfh cells do not help in vivo like recent data suggest they do in vitro. Th1/Tfh significantly generated few GC B cells, compared to Il21+ Tfh-like cells. Recipients of Th1-like cells had significantly lower parasite-specific IgG and GCs by immunohistology than Tfh-like at 21 dpi, hybrid Th1/Tfh were intermediate. A cytokine kinetics study of Th subsets in infected cytokine reporter mouse distinguished Il4+Il21+ GC Tfh from Th1 cells. The inflammation-driven chemokine receptors CXCR3 and CXCR6 are highly expressed on GC Tfh and Th1/Tfh hybrid during the first week of infection, but decline as GCs develop, suggesting a role for T cell migration which could explain the delay in GC formation and parasite-specific antibody production in malaria. Supported by R01AI 135061