Serosal Cavities Contain Two Populations of Innate-like integrin α4highCD4+ T Cells, Integrin α4β1+α6β1+α4β7− and α4β1+α6β1−α4β7+ Cells

We previously reported peritoneal innate-like integrin α4 (CD49d)highCD4+ T cells that provided help for B-1a cells. Here we analyzed the expression of various integrin chains on the peritoneal and pleural integrin α4highCD4+ T cells and investigated the functional heterogeneity of the subpopulations based on the integrin expression. Pleural cavity contained a lower ratio of integrin α4highCD4+ T cells to integrin α4lowCD4+ T cells than peritoneal cavity, but the pleural integrin α4highCD4+ T cells have the same characteristics of the peritoneal integrin α4highCD4+ T cells. Most of integrin α4highCD4+ T cells were integrin β1highβ7-, but a minor population of integrin α4highCD4+ T cells was integrin β1+β7+. Interestingly, the integrin α4highβ1highβ7- CD4+ T cells expressed high levels of integrin α4β1 and α6β1, whereas integrin α4highβ1+β7+ CD4+ T cells expressed high levels of integrin α4β1 and α4β7, suggesting an alternative expression of integrin α6β1 or α4β7 in combination with α4β1 in respective major and minor populations of integrin α4highCD4+ T cells. The minor population, integrin α4highβ1+β7+ CD4+ T cells, were different from the integrin α4highβ1highβ7- CD4+ T cells in that they secreted a smaller amount of Th1 cytokines upon stimulation and expressed lower levels of Th1-related chemokine receptors CCR5 and CXCR3 than the integrin α4highβ1highβ7- CD4+ T cells. In summary, the innate-like integrin α4highCD4+ T cells could be divided into 2 populations, integrin α4β1+α6β1+α4β7- and α4β1+α6β1-α4β7+ cells. The functional significance of serosal integrin α4β7+ CD4+ T cells needed to be investigated especially in view of mucosal immunity.