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Immune dysregulation in human subjects with heterozygous germline mutations in CTLA4

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Science  26 Sep 2014:
Vol. 345, Issue 6204, pp. 1623-1627
DOI: 10.1126/science.1255904

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Beware of T cells that don't know how to stop

During an infection, T cells divide extensively and secrete proteins that can severely damage tissues. But T cells know when to stop—they express proteins on their surface such as CTLA4, which put on the brakes. Kuehn et al. now report genetic evidence of the importance of CTLA4 in humans (see the Perspective by Rieux-Laucat and Casanova). They identified six patients with mutations in one copy of CTLA4. Patients presented with symptoms of an overzealous immune response, with immune cells infiltrating their organs. The findings support the idea that CTLA4 tells the immune system when enough is enough.

Science, this issue p. 1623; see also p. 1560

Abstract

Cytotoxic T lymphocyte antigen–4 (CTLA-4) is an inhibitory receptor found on immune cells. The consequences of mutations in CTLA4 in humans are unknown. We identified germline heterozygous mutations in CTLA4 in subjects with severe immune dysregulation from four unrelated families. Whereas Ctla4 heterozygous mice have no obvious phenotype, human CTLA4 haploinsufficiency caused dysregulation of FoxP3+ regulatory T (Treg) cells, hyperactivation of effector T cells, and lymphocytic infiltration of target organs. Patients also exhibited progressive loss of circulating B cells, associated with an increase of predominantly autoreactive CD21lo B cells and accumulation of B cells in nonlymphoid organs. Inherited human CTLA4 haploinsufficiency demonstrates a critical quantitative role for CTLA-4 in governing T and B lymphocyte homeostasis.

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