Background:Our recent work demonstrated that laminins α4β1γ1 and α5β1γ1, components of the lymph node (LN) stroma, are differentially regulated. Tolerance is associated with relatively higher laminin α4 expression, while immunity is associated with laminin α5 upregulation. These differences resulted in altered regulation of alloreactive T cell and antigen-presenting cell trafficking within and extravasation through high endothelial venules. Here, we tested the hypothesis that laminins directly impact CD4 T cell activation and polarization.

Methods:CD4 T cells from C57BL/6 mice were activated with anti-CD3 with or without laminin α4 and/or α5. The laminin α5 receptor was blocked with anti-α6 integrin mAb. After 3-5 days of culture, proliferation and Foxp3, CD69, CD25, CD44 and CD62L expression were determined by flow cytometry. For in vivo experiments, TCR Tg CD4cells from TEa mice that recognize donor I-E^d presented by recipient I-A^b were transferred with or without anti-α6 integrin mAb into C57BL/6 mice that had received BALB/c donor-specific splenocytes (DST). TEa T cell proliferation and activation were then analyzed.

Results:Addition of laminin α4 to anti-CD3 stimulated cultures reduced CD4 T cell proliferation and activation. In contrast, addition of laminin α5 increased proliferation and activation marker expression by up to 8 fold. Addition of anti-α6 integrin blocking mAb abrogated the stimulatory effect, demonstrating that α6 integrin is the main receptor for laminin α5. Moreover, laminin α5 also reduced the proportion of Treg cells induced by TGF-β by 2 fold. This effect was also abrogated by anti-α6 integrin mAb. The proportion of Treg cells induced by TGF-β was unaltered by the presence of laminin α4. However, addition of laminin α4 was able to partially reverse the inhibitory effect of laminin α5 on Treg induction. In vivo, systemic blockade of α6 integrin resulted in decreased proliferation and activation of alloantigen specific CD4 T cells in the LNs of DST treated recipient mice.

Conclusion:These results demonstrate that the laminin trimers α4β1γ1 and α5β1γ1 are co-inhibitory and co-stimulatory ligands, respectively, for CD4 T cells. Laminin α5β1γ1 is recognized by the integrin a6 expressed by T cells. This confirmed the immunogenic role of this laminin-specific receptor and suggested a co-stimulatory role for laminin α5β1γ1 in vivo. These findings demonstrate that laminins are not only passive LN structural molecules, but act as molecular switches for tolerance and immunity by directly influencing T cell functions.

CITATION INFORMATION: Simon T, Bromberg J. Lymph Node Stromal Laminins Differentially Regulate T Cell Immunity and Tolerance. Am J Transplant. 2016;16 (suppl 3).

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