Constitutive expression of tenascin in T-dependent zones of human lymphoid tissues.

Tenascin is a major extracellular matrix glycoprotein that can interfere with the action of fibronectin by inhibiting cell adhesion and spreading. Although tenascin is able to exert important immunomodulatory activities on T and B cells and macrophages, little is known about its distribution in different lymphohemopoietic tissues. In this study we have analyzed tenascin immunoreactivity on cryostat and paraffin sections of normal and pathological lymphoid tissues using two different monoclonal antibodies. We demonstrated strong tenascin expression in all peripheral lymphoid tissues, whereas it was barely detectable in the thymus and in bone marrow. In reactive lymph nodes, tenascin was mainly found in T-dependent zones, forming a variably close-woven reticular network corresponding to fibroblastic reticulum cells and blood vessels basal laminae, showing a partial co-localization with fibronectin. In B-dependent zones, tenascin was restricted to blood vessels. Using double-marker analysis, we performed a thorough study comparing tenascin expression in different compartments of lymphoid microenvironments. Tenascin network appeared much thicker in chronically stimulated tissues, where CD4+ lymphocytes with "memory" phenotype (CD45RO+/CD45RA-) were predominant, and at sites of ongoing inflammation. In particular, a striking increase of tenascin was observed in sarcoid lymph node, as well as in myasthenic hyperplastic thymuses. In addition, tenascin can be abnormally synthesized in tissue involved by various types of lymphomas, including Hodgkin's disease and hairy cell leukemia.