Regulation of Antigen-Experienced T Cells: Lessons from the Quintessential Memory Marker CD44

Abstract

Despite the widespread use of the cell-surface receptor CD44 as a marker for antigen (Ag)-experienced, effector and memory T cells, surprisingly little is known regarding its function on these cells. The best-established function of CD44 is the regulation of cell adhesion and migration. As such, the interactions of CD44, primarily with its major ligand, the extracellular matrix (ECM) component hyaluronic acid (HA), can be crucial for the recruitment and function of effector and memory T cells into/within inflamed tissues. However, little is known about the signaling events following engagement of CD44 on T cells and how cooperative interactions of CD44 with other surface receptors affect T cell responses. Recent evidence suggests that the CD44 signaling pathway(s) may be shared with those of other adhesion receptors, and that these provide contextual signals at different anatomical sites to ensure the correct T cell effector responses. Furthermore, CD44 ligation may augment T cell activation after Ag encounter and promote T cell survival, as well as contribute to regulation of the contraction phase of an immune response and the maintenance of tolerance. Once the memory phase is established, CD44 may have a role in ensuring the functional fitness of memory T cells. Thus, the summation of potential signals after CD44 ligation on T cells highlights that migration and adhesion to the ECM can critically impact the development and homeostasis of memory T cells, and may differentially affect subsets of T cells. These aspects of CD44 biology on T cells and how they might be modulated for translational purposes are discussed.

Thymic Involution Perturbs Negative Selection Leading to Autoreactive T Cells That Induce Chronic Inflammation

“…1B, left panels, and supplemental Fig. S1B), which represent antigen-experienced T cells (37), and these F-cKO RTEs were more proliferative (Fig. 1B and supplemental Fig.…”

Protein Translation Activity: A New Measure of Host Immune Cell Activation

“…Remarkably, in naïve mice, a minor but clear population of splenic CD44 high CD4 + and CD8 + T cells exhibited increased RPM staining compared to CD44 low T cells (Figure 3, Figure 5, Supplemental Figure 2, Supplemental Figure 3A). CD44 is a T lymphocyte activation marker constitutively and robustly expressed by effector and memory cells (14). In naïve specific pathogen free mice, this population likely represents “innate memory” (IM) T cells, cells with a memory-like phenotype despite no prior exposure to cognate antigen (15).…”

Melatonin controls experimental autoimmune encephalomyelitis by altering the T effector/regulatory balance

“…To our knowledge, this is the first study showing that melatonin treatment decreases the surface expression of the T cell activation marker CD44 in memory populations. These reduced numbers of T EM cells with marked decrease in CD44 expression are likely to be less attracted to the CNS and show impaired CNS-infiltration capacity, since CD44 participates in immune cell adhesion to the endothelium and infiltration into inflamed tissues (Baaten et al, 2012). Additionally, the CNS cytokine milieu in treated animals (reduced levels of IL-1 and TNF) would contribute to reducing both the CD44 activation and the HA presentation in the inflamed endothelium (Bollyky et al, 2007;Jiang et al, 2011).…”