Altered levels of memory T cell subsets and common γc cytokines in Strongyloides stercoralis infection and partial reversal following anthelmintic treatment

Strongyloides ratti infection in mice: immune response and immune modulation

Strongyloides ratti is a natural parasite of wild rats and most laboratory mouse strains are also fully permissive. The infection can be divided into three distinct phases: the tissue migration of the infective third stage larvae during the first two days, the early intestinal establishment of S. ratti parasites molting to adults on days three to six and the later intestinal parasitic phase until the end of infection. Immunocompetent mice terminate the S. ratti infection after one month and are semi-resistant to a second infection. Employing the powerful tools of mouse immunology has facilitated a detailed analysis of the initiation, execution and regulation of the immune response to S. ratti. Here we review the information collected to date on the protective immune response to migrating S. ratti larvae in tissues and to adult parasites in the intestine. We show that depending on the phase of infection, a site-specific portfolio of immune effector mechanisms is required for infection control. In addition, we summarize the strategies employed by S. ratti to evade the immune system and survive long enough in its host to replicate despite an effective immune response. Selected murine studies using the closely related Strongyloides venezuelensis will be discussed. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Modulation of circulating cytokine production in alcoholic patients infected with Strongyloides stercoralis

Strongyloidiasis control is associated with a Th2 immune response. However, alcohol ingestion plays an important role in modulating the immune system. The aim of this study is to evaluate the occurrence of Strongyloides stercoralis infection in alcoholic patients, the levels of circulating cytokines (IFN-γ, IL-2, IL-4, IL-5, IL-10, IL-15 and IL-17), and its correlation with modulation of parasitic load in alcoholic individuals infected with S. stercoralis. A total of 336 alcoholic patients, treated at the Alcoholic Care and Treatment Center were included in this study. The cytokine levels were measured by a commercial ELISA in 80 sera divided into four groups with 20 individuals each: alcoholics infected (ASs+) and not infected (ASs-) with S. stercoralis and non-alcoholics infected (NASs+) and not infected (NASs-) with the helminth. S. stercoralis frequency in alcoholic patients was 16.1% (54/336). The parasitic load varied from 1 to 546 larvae/g of faeces, median and interquartile range (IQR) of 9 and 1.0-62.5 larvae/g of faeces, while in non-alcoholic individuals the parasitic load was less than 10 larvae/g of faeces. Levels of circulating IL-4 were significantly higher in ASs+ when compared with NASs- group (p < .05). An inverse correlation between serum levels of IFN-γ and parasitic load in alcoholic patients infected with S. stercoralis was observed (r = -601; p < 0.01). These results suggest that modulation of IFN-γ production occurs in alcoholic individuals with high parasitic burden.

Association between anti-Anisakis simplex antibodies and interleukin-7 levels

IL-7 is a crucial factor for the development of lymphocytes, and it is absolutely necessary for γδ T cells. Mice deficient in L-7 have a deficit of B and αβ T lymphocytes, and an absence of mature γδ TCR cells. IL-7 is essential for the survival, development and maturation of Schistosoma sp., although its production is associated with protection against intestinal helminths. The presence of anti-Anisakis simplex antibodies, especially IgA, is related to a lower frequency in CD3 + CD56 + αβ + lymphocytes and all subpopulations of γδ T cells. In this work, the relationship of IL-7 with humoral and cellular responses against A. simplex in 100 healthy subjects was studied. We have found significantly higher IL-7 levels in anti-A. simplex IgA-positive subjects (p < 0.001). The positivity of anti-A. simplex IgA was associated with a significant reduction in the frequency of CD3 + αβ+ (p < 0.01), CD3 + CD4 + αβ+, CD3 + CD8 + αβ+, CD3 + CD56 + αβ+, CD3 + γδ+, CD3 + CD4-CD8-γδ+ and CD3 + CD56 + γδ+ (p < 0.05) cells. In the case of NKT cells, this same phenomenon was also associated with IgE positivity. There was a weak inverse correlation (Spearman) of IL-7 levels with the frequencies of CD3 + CD4 + αβ+ (-0.125, p = 0.047), CD3 + CD8 + αβ+ (-0.204, p = 0.032), CD3 + CD56 + αβ+ (-0.247, p = 0.007), CD3 + γδ+ (-0.267, p = 0.007), CD3 + CD4-CD8-γδ+ (-0.266, p = 0.003), and CD3 + CD8 + γδ + (-0.302, p = 0.002) cells. The role of NKT cells in the anti-A. simplex response was confirmed and an association between IL and 7 levels and specific antibodies, especially IgA, was demonstrated. The higher production of IL-7 would represent a compensatory mechanism in response to the reduction in lymphocyte populations associated with the response against this parasite.

Characterization of memory T cell subsets and common γ-chain cytokines in convalescent COVID-19 individuals

T cells are thought to be an important correlates of protection against SARS‐CoV2 infection. However, the composition of T cell subsets in convalescent individuals of SARS‐CoV2 infection has not been well studied. The authors determined the lymphocyte absolute counts, the frequency of memory T cell subsets, and the plasma levels of common γ−chain in 7 groups of COVID‐19 individuals, based on days since RT‐PCR confirmation of SARS‐CoV‐2 infection. The data show that both absolute counts and frequencies of lymphocytes as well as, the frequencies of CD4⁺ central and effector memory cells increased, and the frequencies of CD4⁺ naïve T cells, transitional memory, stem cell memory T cells, and regulatory cells decreased from Days 15–30 to Days 61–90 and plateaued thereafter. In addition, the frequencies of CD8⁺ central memory, effector, and terminal effector memory T cells increased, and the frequencies of CD8⁺ naïve cells, transitional memory, and stem cell memory T cells decreased from Days 15–30 to Days 61–90 and plateaued thereafter. The plasma levels of IL‐2, IL‐7, IL‐15, and IL‐21—common γc cytokines started decreasing from Days 15–30 till Days 151–180. Severe COVID‐19 patients exhibit decreased levels of lymphocyte counts and frequencies, higher frequencies of naïve cells, regulatory T cells, lower frequencies of central memory, effector memory, and stem cell memory, and elevated plasma levels of IL‐2, IL‐7, IL‐15, and IL‐21. Finally, there was a significant correlation between memory T cell subsets and common γc cytokines. Thus, the study provides evidence of alterations in lymphocyte counts, memory T cell subset frequencies, and common γ−chain cytokines in convalescent COVID‐19 individuals.