Lack of ICAM-1 on APCs during T Cell Priming Leads to Poor Generation of Central Memory Cells

Abstract

ICAM-1/LFA-1 interactions are known to enhance T cell/APC interactions and to promote T cell activation and cytokine secretion. We have analyzed the consequences of ICAM-1-mediated signaling on the generation of memory T cell subsets. We report that lack of ICAM-1 on APCs, but not on T cells, leads to poor T cell activation and proliferation in vitro and in vivo, and that the defect can be compensated by Ag dose, exogenous IL-2, additional costimulation, and by increasing responder T cell density on APCs. ICAM-1-null mice do not respond to immunization with OVA peptide, but immunization with OVA or with Salmonella typhimurium leads to good T cell proliferation 7–10 days later, and clearance of a challenge infection is equivalent to that of wild-type mice. However, when followed over time, recall proliferation and antibacterial immunity decay rapidly in ICAM-1-null mice, while recall cytokine responses are unaffected. The decline in immunity is not related to poor survival of T cells activated on ICAM-1-null APCs, or to poor generation of effectors in ICAM-1-null mice. Phenotypic analysis of T cells stimulated on ICAM-1-null APCs reveals preferential generation of CD44highCD62Llow effector memory cells (TEM) over CD44highCD62Lhigh central memory cells (TCM). Further, while the proportion of naive:memory T cells is similar in unmanipulated wild-type and ICAM-1-null mice, there is an accumulation of TEM cells, and a high TEM: TCM ratio in aging ICAM-1-null mice. Together, the data indicate that signaling through LFA-1 during T cell activation may be involved in commitment to a proliferation-competent memory pool.