Phenotypic changes of γδ T cells in Plasmodium falciparum placental malaria and pregnancy outcomes in women at delivery in Cameroon

Introduction: Depending on the microenvironment, gamma delta T cells may assume characteristics similar to those of Th1, Th2, Th17, regulatory T cells or antigen presenting cells. Despite the wide documentation of the effect of Th1/Th2 balance on pregnancy associated malaria and outcomes, there are no reports on the relationship between gamma delta T cell phenotype change and Placental Malaria (PM) with pregnancy outcomes. This study sought to investigate the involvement of gamma delta T cells and its subsets in placental Plasmodium falciparum malaria. Methods:In a case-control study conducted in Yaound & eacute;, Cameroon from March 2022 to May 2023, peripheral, placental and cord blood samples were collected from 50 women at delivery (29 PM negative: PM- and 21 PM positive: PM+; as diagnosed by light microscopy). Hemoglobin levels were measured using hemoglobinometer. PBMCs, IVBMCs and CBMCs were isolated using histopaque-1077 and used to characterize total gamma delta T cell populations and subsets (V delta 1(+), V delta 2(+), V delta 1(-)V delta 2(-)) by flow cytometry. Results: Placental Plasmodium falciparum infection was associated with significant increase in the frequency of total gamma delta T cells in IVBMC and of the V delta 1(+) subset in PBMC and IVBMC, but decreased frequency of the V delta 2(+) subset in PBMC and IVBMC. The expression of the activation marker: HLA-DR, and the exhaustion markers (PD1 and TIM3) within total gamma delta T cells and subsets were significantly up-regulated in PM+ compared to PM- group. The frequency of total gamma delta T cells in IVBMC, TIM-3 expression within total gamma delta T cells and subsets in IVBMC, as well as HLA-DR expression within total gamma delta T cells and V delta 2(+) subset in IVBMC were negatively associated with maternal hemoglobin levels. Furthermore, the frequency of total gamma delta T cells in PBMC and PD1 expression within the V delta 2(+) subset in CBMC were negatively associated with birth weight contrary to the frequency of V delta 1(-)V delta 2(-) subset in PBMC and HLA-DR expression within the V delta 2(+) subset in IVBMC which positively associated with maternal hemoglobin level and birth weight, respectively. Conclusion: The data indicate up-regulation of activated and exhausted gamma delta T cells in Plasmodium falciparum placental malaria, with effects on pregnancy outcomes including maternal hemoglobin level and birth weight.