Human endothelial cell presentation of antigen and the homing of memory/effector T cells to skin.
Dermal microvascular endothelial cells (ECs) form a continuous lining that normally bars blood-borne T lymphocytes from entering the skin, but as part of the response to foreign antigen, dermal ECs undergo alterations in their surface proteins so as to provide signals to circulating T cells that lead to their activation and recruitment. Several observations suggest that human dermal microvascular ECs may help initiate cutaneous immune reactions by presentation of cognate antigens to circulating T memory cells: (1) antigen-specific inflammatory responses in the skin, as in other organs, involve accumulation of memory and effector T cell populations that are enriched in cells specific for the eliciting antigen; (2) recall responses to intradermal protein antigens in the skin start very rapidly within two hours of challenge; (3) dermal microvascular ECs in humans and other large mammals basally display high levels of class I and class II MHC molecules, the only known purpose of which is to present antigenic peptides to lymphocytes; (4) the lumen of dermal capillaries are narrower than the diameter of circulating T cells, ensuring surface contact; and (5) cultured human ECs effectively present antigens to resting memory T cells isolated from the circulation. Upon contact with activated T cells or their secreted products (cytokines), dermal ECs themselves become activated, increasing their capacity to recruit memory and effector T cell populations in an antigen-independent manner. Specifically, activated ECs express inducible leukocyte adhesion molecules such as E-selectin, ICAM-1, and VCAM-1; and several lines of evidence, including neutralizing antibody experiments and gene knockouts, have supported a role of these molecules in T cell recruitment. Dermal ECs have unique expression patterns of adhesion molecules that can determine the subsets of memory T cells that are recruited into the skin. For example, slow internalization of E-selectin allows more persistent expression of this protein on the surface of dermal ECs, favoring interactions with CLA-1+ T cells. VCAM-1 expression, normally confined to venular EC may extend to capillaries within the dermal papillae and contribute to epidermal inflammation, recruiting alpha4beta7 integrin-expressing T cells that also express the cadherin-binding integrin alphaEbeta7. New models involving transplantation of normal and genetically modified human dermal ECs into immunodeficient mice may be used to further explore these properties.
Pober
J S
JS
Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut 06510, USA. jordan.pober@yale.edu
Kluger
M S
MS
Schechner
J S
JS
D000818:Animals; D017951:Antigen Presentation; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002465:Cell Movement; D004730:Endothelium, Vascular / Q000276:immunology*; D006801:Humans; D007156:Immunologic Memory; D016410:Lymphoma, T-Cell, Cutaneous / Q000276:immunology; D051379:Mice; D023421:Models, Animal; D012867:Skin / Q000098:blood supply / Q000276:immunology*; D012878:Skin Neoplasms / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D015815:Cell Adhesion Molecules