Distribution of Laminin Variants and Their Integrin Receptors in Human Secondary Lymphoid Tissue: Colocalization suggests that the α6β4-integrin is a receptor for laminin-5 in lymphoid follicles

Abstract

Laminins are a family of multifunctional basement membrane glycoproteins. Over the last years, many laminin isoforms have been characterized, which were shown to be composed of distinct combinations of variant α β and γ chains. Some of these isoforms show remark-able tissue specificity, which suggests functional involvement in local processes. In this study the previously described mAb 4C7. which recognize epithelial basement membranes as well as endothelial basement membranes in lymphoid follicles, was identified as an anti-laminin-5 antibody. Using a set of mAbs against various variant laminin chains we established that specifically the γ₂ chain of laminin-5 was confined to the endothelial basement membranes of vessels in lymphoid follicles, whereas other variant laminin chains were also expressed elsewhere in the lymphoid tissue. Additionally. the expression of the known integrin receptors of laminin-5 was also examined. The α6β4 integrin-receptor for laminin was found to be colocalized with the laminin-5 γ₂ chain on the abluminal surface of endothelial cells, whereas the α3 integrin chain could not be detected in lymphoid follicles. This finding suggests that the α6β4 integrin (and not the α3β1 integrin) serves as a laminin-5 receptor on endothelial cells in the follicular compartment of lymphoid tissue. Furthermore, α6β4 was also found in the same punctuated pattern on FDCs as laminin-5. The function of the laminin-α6β4 complex in this particular localisation is still obscure, but a role in the maintainance of the follicular compartment via hemidesmosome-like attachment sites is postulated.

Key Words:

• laminin-5
• integrins
• lymphoid tissue
• lymphoid follicle