Abstract for presentation at Australia and New Zealand Society of Nephrology Annual Scientific Conference

Antigens are recognized in the kidney in normal, autoimmune and alloimmune responses. In addition to antigenic peptides/Class II on antigen presenting cells, costimulatory signals are required for activation of CD4+ cells but little is known of the expression/requirement for costimulatory molecules on renal dendritic cells (DCs) in CD4+ cell activation. The phenotype of renal DCs and draining lymph node (DLN) DCs was studied (flow cytometry) before and 24h after intrarenal ovalbumin (OVA) injection with concurrent subcutaneous injection of Freund’s Complete Adjuvant. Digested kidneys/DLNs were enriched for CD11c+ cells (MACS system), and analyzed by gating on CD11c+ cells. A small proportion of “resting” renal DCs expressed CD80, CD86, both, or CD40. PD-L1 was expressed by some DCs, PD-L2 by a greater proportion. After 24h more DCs were expressing costimulatory molecules (Table, *P<0.05). The function of these molecules was studied using OVA-specific TcR transgenic (OT-II) mice. Naive CFSE-labeled OT-II cells were transferred to C57BL/6 mice. After intrarenal antigen injection, DLN were collected (72h) and CD4+ cell proliferation studied by serial halving of CFSE fluorescence. Blocking CD80, CD86, or both, demonstrated that CD86 is important in CD4+ cell proliferation, and anti-CD86/anti-CD80 together had more effect. OT-II cells transferred to CD40-/- mice showed a minor role for CD40. Blocking PD-1 showed that PD-1 negatively regulates proliferation and antigen-specific intracellular IFN-g production. These studies demonstrate that costimulatory molecules are upregulated on renal DCs after stimulation, CD86 is a key early activator of CD4+ cells, and interactions between PD-1 and PD-L1/PD-L2 are important in regulating activation.