Modulation of Monocyte and T Cell Functions by Immune Inhibitory Receptors during Subclinical Malaria

ABSTRACT Subclinical Plasmodium falciparum (Pf) malaria involves the tolerance of parasitemia without development of fever or overt symptoms. Individuals with subclinical malaria are a reservoir for ongoing transmission and are therefore an important target population for malaria elimination strategies. The immunoregulatory mechanisms that permit subclinical Pf infections remain poorly understood. Evidence suggests that immune inhibitory signaling pathways are key to maintaining a sufficient balance between protection from immunopathology while limiting parasite replication. We propose to study the impact of inhibitory receptor signaling on monocyte and T cell functional interactions during transient vs. chronic subclinical malaria in children. We will focus on the role of inhibitory receptors Leukocyte Immunoglobulin Like Receptors B1 (LILRB1) and LILRB2. Our preliminary data show that malaria infections are associated with increased expression of LILRB1 and LILRB2 on monocytes in young children, and engagement of these receptors impairs innate immune cells’ ability to activate T cells. We will leverage already-collected samples from a longitudinal cohort of Beninese children aged 1-15 years to test our central hypothesis that inhibitory receptor signaling in monocytes constrains innate immune functions and suppresses T cell activation during chronic subclinical malaria. In Aim 1, we will (i) define the immunoregulatory phenotypes, including surface expression of co-inhibitory and co-stimulatory receptors on monocytes and T cells, (ii) determine monocyte function following in vitro stimulation and (iii) perform monocyte and T cell transcriptomic analysis (scRNAseq and RTqPCR). We will compare those data between Pf-uninfected children vs. transient subclinical malaria vs. chronic subclinical malaria vs. children with clinical malaria. In Aim 2, we will account for host and parasite factors that may also influence immunoregulatory phenotypes. HLA-G (HLA class I molecule) is a soluble host protein that binds to LILRB1/B2. Level of HLA-G is known to increase during acute malaria. Certain members of the rif multigene family (encoding RIFINs) have recently been shown to bind to LILRB1 and LILRB2, acting as a mimic of HLA-G. Levels of HLA-G and RIFIN variants and their impact on innate immune cellular functions have not been explored in subclinical malaria. We will decipher HLA-G/RIFIN/LILRB interplay and their association with transient and chronic subclinical malaria. These results will further our understanding of naturally acquired immunity and can be used to inform malaria vaccine strategies.