Patency of Litomosoides sigmodontis infection depends on Toll‐like receptor 4 whereas Toll‐like receptor 2 signalling influences filarial‐specific CD4⁺ T‐cell responses

Abstract

Summary BALB/c mice develop a patent state [release of microfilariae (Mf), the transmission life‐stage, into the periphery] when exposed to the rodent filariae Litomosoides sigmodontis. Interestingly, only a portion of the infected mice become patent, which reflects the situation in human individuals infected with Wuchereria bancrofti. Since those individuals had differing filarial‐specific profiles, this study compared differences in immune responses between Mf+ and Mf– infected BALB/c mice. We demonstrate that cultures of total spleen or mediastinal lymph node cells from Mf+ mice produce significantly more interleukin‐5 (IL‐5) to filarial antigens but equal levels of IL‐10 when compared with Mf– mice. However, isolated CD4+ T cells from Mf+ mice produced significantly higher amounts of all measured cytokines, including IL‐10, when compared with CD4+ T‐cell responses from Mf– mice. Since adaptive immune responses are influenced by triggering the innate immune system we further studied the immune profiles and parasitology in infected Toll‐like receptor‐2‐deficient (TLR2−/−) and TLR4−/− BALB/c mice. Ninety‐three per cent of L. sigmodontis‐exposed TLR4−/− BALB/c mice became patent (Mf+) although worm numbers remained comparable to those in Mf+ wild‐type controls. Lack of TLR2 had no influence on patency outcome or worm burden but infected Mf+ mice had significantly lower numbers of Foxp3+ regulatory T cells and dampened peripheral immune responses. Interestingly, in vitro culturing of CD4+ T cells from infected wild‐type mice with granulocyte–macrophage colony‐stimulating factor‐derived TLR2−/− dendritic cells resulted in an overall diminished cytokine profile to filarial antigens. Hence, triggering TLR4 or TLR2 during chronic filarial infection has a significant impact on patency and efficient CD4+ T‐cell responses, respectively.

Absence of IL-17A in Litomosoides sigmodontis-infected mice influences worm development and drives elevated filarial-specific IFN-γ

“…FACS staining was performed as previously described (Rodriogo et al 2016). In brief, cells were fixed and permeabilised with intracellular fixation and permeabilisation buffer set (Thermo Fisher Scientific) according to the manufacturer’s instructions.…”

“…Primers 1 and 2 were used to detect wildtype allele (1.3 kb), and primers 1 and 3 were used to detect mutant allele (0.5 kb) (Nakae et al 2002 ). The life cycle of L. sigmodontis was maintained in house using infected cotton rats and recovered adult worms were used as the source of L. sigmodontis antigen (LsAg) preparation (Rodriogo et al 2016 ). Protein concentrations of antigenic extracts were determined using the Advanced Protein Assay (Cytoskeleton, ORT, USA) and aliquots of sterile LsAg were frozen at − 80 °C until required.…”

“…Absolute cell counts from the mLN and TC of individual mice were determined using the CASY® Cell Counter and Analyser System Model TT (Roche Innovatis AG, Reutlingen, Germany). FACS staining was performed as previously described (Rodriogo et al 2016 ). In brief, cells were fixed and permeabilised with intracellular fixation and permeabilisation buffer set (Thermo Fisher Scientific) according to the manufacturer’s instructions.…”

Infection-Derived Monocytic MDSCs Require TGF-β to Suppress Filarial-Specific IFN-γ But Not IL-13 Release by Filarial-Specific CD4+ T Cells In Vitro

“…To understand mechanisms underlying immunity to filarial infections in man, such as Wuchereria bancrofti which elicits lymphatic filariasis (LF) (2,3), researchers employ the Litomosoides sigmodontis (L. sigmodontis, Ls) rodent model since it reflects several aspects of LF infection. This includes partial patency since only a portion of immunocompetent BALB/c mice become patent (release microfilariae (MF) into the periphery) when naturally infected with Ls (4)(5)(6). The development of adult worms from larval stages in the host provokes different immune reactions and encompasses both innate (neutrophils, eosinophils and basophils) and adaptive responses (T and B cells).…”

Human filariasis—contributions of the Litomosoides sigmodontis and Acanthocheilonema viteae animal model

“…Moreover, the L. sigmodontis mouse model has been instrumental in understanding the role of Wolbachia beyond the mutualistic relationship with the parasite itself. For example, several studies showed that Toll-like and nucleotide-binding oligomerization domain (NOD)–like receptors and downstream signalling pathways are important for sensing Wolbachia , worm development, MF embryogenesis, and immunity against filariae (Pfarr et al 2003 ; Brattig et al 2004 ; Ajendra et al 2016 ; Rodrigo et al 2016 ; Wiszniewsky et al 2019 ). For a more in-depth review of immune responses to L. sigmodontis in mice, we refer the reader to the recent review by Finlay and Allen ( 2020 ).…”