ANTI-ASIALO GM1 TREATMENT DURING SECONDARY TOXOPLASMA GONDII INFECTION IS LETHAL AND DEPLETES T CELLS

Abstract

Abstract Anti-NK1.1 and anti-Asialo GM1 (ASGM1) antibodies are used to deplete NK cells. Many antibody depletion strategies in vivo can have off-target effects. In a vaccine challenge model of T. gondii infection, we observed treatment of mice with these antibodies resulted in different survival outcomes after lethal secondary infection. Anti-ASGM1 resulted in 100% death and greater parasite burden at the site of infection than anti-NK1.1 treatment. We also found that anti-ASGM1 treatment depleted T cells. While both CD8+ and CD4+ T cells were affected, CD8+ T cells were more susceptible to the anti-ASGM1 treatment. Surface ASGM1 of the T cells was expressed on a higher percentage of CD8+ T cells than CD4+ T cells. Not all CD8+ T cells expressed ASGM1. In immunized mice ASGM1 was highly enriched on the surface of effector memory (Tem) and central memory (Tcm) CD8+ T cells, with a greater effect on Tem cells. After secondary parasite challenge, Tem, Tcm, effector (Tef) and naïve (Tn) CD8+ T cells were positive for ASGM1. Anti-ASGM1 treatment during rechallenge resulted in greater depletion of activated IFNγ+, Granzyme B+, Tem and Tef than Tcm and Tn CD8+ T cells. In addition, anti-ASGM1 depleted IFNγ+ CD4+ T cells. Recombinant IFNγ supplementation prolonged the survival of anti-ASGM1 treated mice, demonstrating that anti-ASGM1 eliminated IFNγ-producing T and NK cells important for control of the parasite. Our results thus highlight that anti-ASGM1 is not an optimal choice for targeting only NK cells and more precise approaches should be used to target them. This study also uncovers ASGM1 as a marker of activated effector T cells and the potential importance of changes in sialylation in lipid rafts for T cell activation during T. gondii infection.