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Inhibitory Receptors and Pathways of Lymphocytes

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Front. Immunol. | doi: 10.3389/fimmu.2018.02994

CD6, a rheostat-type signalosome that tunes T cell activation

  • 1i3S, Instituto de Investigação e Inovação em Saúde, Portugal

FFollowing T cell receptor triggering, T cell activation is initiated and amplified by the assembly at the TCR/CD3 macrocomplex of a multitude of stimulatory enzymes that activate several signaling cascades. The potency of signaling is, however, modulated by various inhibitory components already at the onset of activation, long before co-inhibitory immune checkpoints are expressed to help terminating the response. CD5 and CD6 are surface glycoproteins of T cells that have determinant roles in thymocyte development, T cell activation and immune responses. They belong to the superfamily of scavenger receptor cysteine-rich (SRCR) glycoproteins but whereas the inhibitory role of CD5 has been established for long, there is still controversy on whether CD6 may have similar or antagonistic functions on T cell signaling. Analysis of the structure and molecular associations of CD5 and CD6 indicates that these molecules assemble at the cytoplasmic tail a considerable number of signaling effectors that can putatively transduce diverse types of intracellular signals. Biochemical studies have concluded that both receptors can antagonize the flow of TCR-mediated signaling; however, the impact that CD5 and CD6 have on T cell development and T cell-mediated immune responses may be different. Here we analyze the signaling function of CD6, the common and also the different properties it exhibits comparing with CD5, and interpret the functional effects displayed by CD6 in recent animal models.

Keywords: inhibitory receptors, CD5, CD6, signalosome, T lymphocytes

Received: 31 Jul 2018; Accepted: 04 Dec 2018.

Edited by:

Bernard Malissen, INSERM U1104 Centre d'immunologie de Marseille-Luminy, France

Reviewed by:

Jacques A. Nunes, INSERM U1068 Centre de recherche en cancérologie de Marseille, France
Renaud Lesourne, INSERM U1043 Centre de Physiopathologie de Toulouse Purpan, France  

Copyright: © 2018 Gonçalves, Henriques, Santos and Carmo. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Alexandre M. Carmo, i3S, Instituto de Investigação e Inovação em Saúde, Porto, 4200-135, Porto, Portugal, acarmo@ibmc.up.pt