Non-additive strong gene interactions cause striking differences in organ pathology and cytokine response in leishmaniasis

Yahya Sohrabi^1,2,3Tatyana Kobets²Valeriya Volkova²Eliska Javorkova⁴Imtissal Krayem²Alena Zajicova⁴Helena Havelkova²Milena Svobodova⁵Vladimir Holan⁶Peter Demant⁷Marie Lipoldova^1*Imtissal Krayem²

• ¹Third Faculty of Medicine, Charles University, Prague, Czechia
• ²Laboratory of Molecular and Cellular Immunology, Institute of Molecular Genetics, Prague, Prague, Czechia
• ³Department of Cardiology I, University Hospital Münster, Münster, North Rhine-Westphalia, Germany
• ⁴Department of Nanotoxicology and Molecular Epidemiology, Institute of Experimental Medicine (ASCR), Prague, Prague, Czechia
• ⁵Department of Parasitology, Faculty of Science, Charles University, Prague, Czechia
• ⁶Department of Nanotoxicology and Molecular Epidemiology, Institute of Experimental Medicine CAS, Prague, Czechia
• ⁷Department of Molecular and Cellular Biology, Roswell Park Comprehensive Cancer Center, University at Buffalo, Buffalo, New York, United States

The mouse strain O20 is highly resistant to parasite Leishmania major. O20 mice differed from all resistant strains tested until now, as they harbored parasites in their organs, but upon exposure to soluble Leishmania antigen (SLA) their splenocytes did not respond by cytokine production and their macrophages did not produce NO, suggesting a novel mechanism of resistance. Another resistant strain C57BL/10 (B10) harbors similar numbers of parasites as O20 in its organs and its splenocytes respond to SLA by production of IFNγ, but not IL-4. They also produce IL-2, IL-6, IL-10 and IL-17. Macrophages respond to SLA by NO production. Strain B10.O20 was derived from a cross of these two resistant strains. B10 provided 96.4 % of its genome and O20 contributed 3.6 % of its genome. Unexpectedly, this very limited difference between the two strains resulted in the very large phenotypic effects. B10.O20 was susceptible to L. major, as it exhibited large skin lesions, high parasite numbers in skin and lymph nodes, and a massive spleen infiltration by CD11b + CD193 + and CD11b + Gr1 + cells. Thus, a small percentage of genes of the resistant strain O20 in the genome of the second resistant strain B10 resulted in high susceptibility to L. major. After stimulation with SLA, splenocytes of B10.O20 produced significantly higher level of all Th1, Th2 and Th17 cytokines than both its parental strains B10 and O20. This suggested a chronic inflammation with imbalance of several arms of immune response.In summary, the responses of strains B10.O20 and O20 to L. major revealed novel disease phenotypes that have not been observed previously in mice but they were seen in several clinical studies of human leishmaniasis. The studies of heterogeneity of defensive strategies of mouse strains may guide development of effective 3 antileishmanial therapies or vaccine development and it could serve as a basis for 51 investigation of asymptomatic responses to other infectious diseases.