Mechanisms of CD4 T cell help to myeloid cells in tuberculosis

ABSTRACT CD4 T cells govern host control of M. tuberculosis (Mtb) infection. The diverse phagocytic myeloid cells that harbor intracellular Mtb in the lungs require CD4 T cell help to activate antibacterial effector mechanisms. Protection against tuberculosis (TB) depends on this cellular interaction, but it remains incompletely defined. In our preliminary studies, we discovered that myeloid cells in the lungs of Mtb infected mice critically depend on T cells to deploy a broad program of transcriptional activity that controls intracellular infection. These pathways, constituting the spectrum of T cell help, included some pathways known to be due to adaptive immune function, but also others that are canonically considered innate. Despite the heterogeneity of myeloid cells in the lungs, most T cell dependent pathways were shared by MHCII+ antigen presenting cells (APCs) and non-antigen presenting cells, like neutrophils. Using adoptive transfer, we found that CD4 T cells were both necessary and sufficient for induction of the acute inflammatory response by MHCII+ APCs, as marked by expression of SAA3. Concordantly, we found that expression of MHCII by monocyte derived APCs was required for control of Mtb in the lungs. To advance understanding of how cell-cell contact mediated by immune synapse formation between CD4 T cells and Mtb-infected APCs contributes to protection, we developed a technique to identify and isolate physically interacting CD4+, MHCII+ multiplets from the lungs. With these preliminary data and tools, we now aim to define mechanisms of CD4 T cell help in TB, characterized as either direct (local, requiring cell-cell contact with APCs) or indirect (global, impacting both APCs and non-APCs). Using adoptive transfer of CD4 T cells from wild type or knockout mice into T cell deficient recipients, we will define how distinct CD4 T cell-derived effector functions drive myeloid cell activation and control of intracellular Mtb among APCs and non-APCs. By advancing our studies of mice that lack MHCII among monocyte derived APCs in the lungs, we will newly define how of antigen presentation in the lungs drives different CD4 T cell functions and determine whether this differs depending on the antigen recognized. We will test the hypothesis that antigen presentation by monocyte derived APCs governs mechanisms of both direct and indirect help. With our innovative approach to isolating physically interacting multiplets composed of CD4 effector T cells and Mtb-infected MHCII+ cells, we will discover bidirectional gene expression programs that are highly associated with immune synapse formation in the lungs. We will use ChipCytometry on sorted multiplets to spatially characterize the protein expression characteristics of each cell contributing to the synapse. Using bone marrow chimeric mice, combined with bulk and multiplet-RNA-Seq, we will determine the role and requirement of essential CD4 T cell effector functions in direct CD4 T cell help delivered at the immune synapse. By providing new information about the ways that CD4 T cells protect the host against TB, the studies will inform and accelerate the development of more effective TB vaccines.