Insights into the possible role of IFNG and IFNGR1 in Kala-azar and Post Kala-azar Dermal Leishmaniasis in Sudanese patients

Post kala-azar dermal leishmaniasis: A threat to elimination program

Leishmaniasis remains a public health concern around the world that primarily affects poor folks of the developing world spanning across 98 countries with mortality of 0.2 million to 0.4 million annually. Post kala-azar dermal leishmaniasis (PKDL) is the late skin manifestation of visceral leishmaniasis (VL). It has been reported that about 2.5% to 20% of patients recovered from VL develop PKDL having stilted macular or nodular lesions with parasites. In the Indian subcontinent (ISC), it manifests a few months after recovery from VL, though in Africa it can occur simultaneously with VL or a little later. New cases of PKDL are also observed without prior VL in the ISC. These individuals with PKDL represent an important but largely neglected reservoir of infection that perpetuates anthroponotic Leishmania donovani transmission in the ISC and can jeopardize the VL elimination program as these cases can infect the sand flies and spread the endemic. Therefore, it becomes imperative to eradicate PKDL as a part of the VL elimination program. With the limited treatment options besides little knowledge on PKDL, this review stands out in focusing on different aspects that should be dealt for sustained VL elimination.

In vitro and in vivo immunomodulatory properties of octyl-β-D-galactofuranoside during Leishmania donovani infection

BACKGROUND

The chemotherapeutic arsenal available to treat visceral leishmaniasis is currently limited, in view of many drawbacks such as high cost, toxicity or emerging resistance. New therapeutic strategies are particularly needed to improve the management and the outcome in immunosuppressed patients. The combination of an immunomodulatory drug to a conventional anti-Leishmania treatment is an emerging concept to reverse the immune bias from Th2 to Th1 response to boost healing and prevent relapses.

METHODS

Here, immunostimulating and leishmanicidal properties of octyl-β-D-galactofuranose (Galf) were assessed in human monocyte-derived macrophages (HM) and in a murine model, after challenge with Leishmania donovani promastigotes. We recorded parasite loads and expression of various cytokines and immune effectors in HM and mouse organs (liver, spleen, bone marrow), following treatment with free (Galf) and liposomal (L-Galf) formulations.

RESULTS

Both treatments significantly reduced parasite proliferation in HM, as well as liver parasite burden in vivo (Galf, P < 0.05). Consistent with in vitro results, we showed that Galf- and L-Galf-treated mice displayed an enhanced Th1 immune response, particularly in the spleen where pro-inflammatory cytokines TNF-α, IL-1β and IL-12 were significantly overexpressed compared to control group. The hepatic recruitment of myeloid cells was also favored by L-Galf treatment as evidenced by the five-fold increase of myeloperoxidase (MPO) induction, which was associated with a higher number of MPO-positive cells within granulomas. By contrast, the systemic level of various cytokines such as IL-1β, IL-6, IL-17A or IL-27 was drastically reduced at the end of treatment.

CONCLUSIONS

Overall, these results suggest that Galf could be tested as an adjuvant in combination with current anti-parasitic drugs, to restore an efficient immune response against infection in a model of immunosuppressed mice.

Population genetic evidence for positive and purifying selection acting at the human IFN-γ locus in Africa

Despite its critical role in the defense against microbial infection and tumor development, little is known about the range of nucleotide and haplotype variation at IFN-γ, or the evolutionary forces that have shaped patterns of diversity at this locus. To address this gap in knowledge, we examined sequence data from the IFN-γ gene in 1461 individuals from 15 worldwide populations. Our analyses uncovered novel patterns of variation in distinct African populations, including an excess of high frequency-derived alleles, unusually long haplotype structure surrounding the IFN-γ gene, and a "star-like" genealogy of African-specific haplotypes carrying variants previously associated with infectious disease. We also inferred a deep time to coalescence of variation at IFN-γ (~ 0.8 million years ago) and ancient ages for common polymorphisms predating the evolution of modern humans. Taken together, these results are congruent with a model of positive selection on standing variation in African populations. Furthermore, we inferred that common variants in intron 3 of IFN-γ are the likely targets of selection. In addition, we observed a paucity of non-synonymous substitutions relative to synonymous changes in the exons of IFN-γ in African and non-African populations, suggestive of strong purifying selection. Therefore, we contend that positive and purifying selection have influenced levels of diversity in different regions of IFN-γ, implying that these distinct genic regions are, or have been, functionally important. Overall, this study provides additional insights into the evolutionary events that have contributed to the frequency and distribution of alleles having a role in human health and disease.