Characterization of mouse CD6 with novel monoclonal antibodies which enhance the allogeneic mixed leukocyte reaction

Abstract

Human CD6 is a cell surface protein expressed by thymocytes, mature T cells, a subset of B cells and certain cells of the brain. On human T cells, CD6 has been shown to act as a co-stimulatory molecule which modulates T cell receptor (TCR)-mediated T cell activation. To study further the recently identified mouse CD6 (mCD6), we generated and characterized a set of anti-mCD6 mAb. Anti-mCD6 mAb recognizing the mCD6 scavenger receptor cysteine-rich (SRCR) extracellular domains 1 and 3 were identified. mAb against SRCR domain 3, but not domain 1, inhibited the interaction of CD6 with a recently identified ligand, activated leukocyte cell adhesion molecule (ALCAM). Immunohistochemical analysis indicated that mCD6 expression was largely localized to the T cell areas of lymphoid tissue and, as previously reported in the human, CD6 was also expressed by neurons. CD6 was highly expressed on mouse T cells isolated from the spleen, lymph node and thymus as demonstrated by two-color immunofluorescence analysis. The CD4+ and CD8+ cells in these lymphoid compartments expressed similar levels of CD6. Immunoprecipitation studies showed that mouse thymocytes predominantly express a CD6 isoform of approximately 130 kDa, while splenocytes predominantly express a CD6 isoform of approximately 100 kDa. Anti-mCD6 mAb enhanced allogeneic mixed leukocyte reactions (MLR), indicating that CD6-ALCAM interactions may regulate the proliferative capacity of T cells.

Frontline: Optimal T cell activation requires the engagement of CD6 and CD166

“…Thus the functional effects observed are best interpreted as blocking CD6/ CD166 and hence affecting the movement of CD6 on the T cell surface when in contact with CD166-positive cells such as APC. In contrast both nonblocking and blocking CD6 mAb [12] enhance the mixed lymphocyte response consistent with the mAb exerting their effects by crosslinking CD6 and having effects on signaling.…”

“…1A), each containing three extracellular SRCR domains, a transmembrane region and cytoplasmic tails well-suited for signal transduction. Expression of CD5 and CD6 appears to be coordinately regulated [11][12][13]. Both are primarily expressed by thymocytes and mature T cells [1,2].…”

“…Functionally, experiments with CD5 and CD6 mAb have suggested a costimulatory role for both these accessory proteins [12,[16][17][18]. However, CD5-deficient mice show that CD5 negatively regulates antigen receptor-mediated signals [19,20].…”

“…Currently there are no data to propose a functional role for the engagement of these molecules. The use of whole antibodies have not been sufficient to address this as both nonblocking and blocking [12] CD6 mAb enhance the mixed lymphocyte response consistent with the mAb exerting their effects by cross-linking CD6 and influencing signaling. In addition to its ability to bind CD6, CD166 mediates homotypic CD166/CD166 interactions [27,28].…”

IRF-3-dependent and augmented target genes during viral infection

“…27 Secreted cytokines and chemokines can recruit other immune cells to the infection site, and cell adherence may be stimulated by the IRF-3-dependent production of the adhesion molecule CD166 (ALCAM) as well as T-cell proliferation. 28 IRF-3 was also found to be necessary for induction of non-classical major histocompatability class I genes Q-I, T-10 and T-22. The non-classical major histocompatability class I proteins serve as ligands for receptors on natural killer cells and g/d T cells.…”