Biomedical subjects

Alexander Khoruts

Publications and source records attributed to Alexander Khoruts.

7 recordsLinked to original sources

PubMed2006

Naive and memory CD4+ T cell survival controlled by clonal abundance.

Immunity to a plethora of microbes depends on a diverse repertoire of naïve lymphocytes and the production of long-lived memory cells. We present evidence here that low clonal abundance in a polyclonal repertoire favors the survival and activation of naïve CD4(+) T cells as well as the survival of their memory cell progeny. The inverse relation between clonal frequency and survival suggests that intraclonal competition could help maintain an optimally diverse repertoire of T cells and an optimal environment for the generation of long-lived memory cells.

Adoptive Transfer↗

PubMed2005

A model of suppression of the antigen-specific CD4 T cell response by regulatory CD25+CD4 T cells in vivo.

Despite intense recent interest, the suppressive mechanisms of regulatory CD25+CD4 T cells remain poorly understood. One deficiency in the field is the lack of in vivo models where the effects of regulatory CD25+CD4 T cells on antigen-specific responder T cells can be measured quantitatively. We describe one such model here. We compared responses of adoptively transferred naive wild-type antigen-specific CD4 T cells in syngeneic CD28-/- and wild-type recipient mice toward a nominal antigen. The cells exhibited a greater degree of proliferation and differentiation in CD28-/- mice and could not be rendered functionally hyporesponsive by systemic exposure to adjuvant-free antigen. The only reason we were able to find to explain this difference was the deficiency of regulatory CD25+CD4 T cells in the CD28-/- mice. Use of CD28-/- mice as adoptive transfer recipients provides a simple model that reveals the contribution of regulatory CD25+CD4 T cells in controlling antigen-driven responses in vivo.

Animals↗

PubMed2004

A causal link between lymphopenia and autoimmunity.

It is well recognized that the composition of the mature T cell population is subject to strict homeostatic control. The TCR repertoire and relative proportions of various T cell subsets are established in the thymus, and continue to be shaped and regulated in the periphery. As the thymic function declines, peripheral homeostatic mechanisms assume increasing importance. Indeed, loss of thymic function does not lead to progressive decline of T cell numbers because peripheral mechanisms ensure that the size of the T cell population is maintained due to proliferation of residual cells. However, our current understanding of the basic mechanisms of 'homeostatic' or lymphopenia-induced proliferation suggests that this drive to maintain population size may be accompanied by loss of TCR diversity and emergence of auto-reactive effector T cells. This prediction is supported by experimental and clinical evidence. This consideration is important because lymphopenia is seen commonly in clinical practice as a consequence of viral infections, or medical treatment of cancer, autoimmunity, and graft rejection. Lymphopenia may be a simple link between viral infections and autoimmunity, and may be one reason for common failure of very potent, but non-specific, immunosuppressive drugs in current clinical use.

Animals↗

PubMed2004

A role for CD28 in lymphopenia-induced proliferation of CD4 T cells.

The peripheral mechanisms that regulate the size and the repertoire of the T cell compartment during recovery from a lymphopenic state are incompletely understood. In particular, the role of costimulatory signals, such as those provided by CD28, which have a critical importance for the immune response toward foreign Ags in nonlymphopenic animals, has been unclear in lymphopenia-induced proliferation (LIP). In this study, we show that accumulation of highly divided CD4 T cells characterized by great potential to make IFN-gamma is significantly delayed in the absence of B7:CD28 costimulation during LIP. Furthermore, CD28-sufficient CD4 T cells show great competitive advantage over CD28-deficient CD4 T cells when transferred together into the same lymphopenic hosts. Administration of CTLA-4-Ig removed this competitive advantage. Interestingly, CTLA-4-Ig treatment resulted in modest inhibition of LIP by CD28-deficient responders, suggesting that some of its effects may be independent of mere B7 blockade.

Abatacept↗

PubMed2004

CD4+ T cell depletion during all stages of HIV disease occurs predominantly in the gastrointestinal tract.

The mechanisms underlying CD4(+) T cell depletion in human immunodeficiency virus (HIV) infection are not well understood. Comparative studies of lymphoid tissues, where the vast majority of T cells reside, and peripheral blood can potentially illuminate the pathogenesis of HIV-associated disease. Here, we studied the effect of HIV infection on the activation and depletion of defined subsets of CD4(+) and CD8(+) T cells in the blood, gastrointestinal (GI) tract, and lymph node (LN). We also measured HIV-specific T cell frequencies in LNs and blood, and LN collagen deposition to define architectural changes associated with chronic inflammation. The major findings to emerge are the following: the GI tract has the most substantial CD4(+) T cell depletion at all stages of HIV disease; this depletion occurs preferentially within CCR5(+) CD4(+) T cells; HIV-associated immune activation results in abnormal accumulation of effector-type T cells within LNs; HIV-specific T cells in LNs do not account for all effector T cells; and T cell activation in LNs is associated with abnormal collagen deposition. Taken together, these findings define the nature and extent of CD4(+) T cell depletion in lymphoid tissue and point to mechanisms of profound depletion of specific T cell subsets related to elimination of CCR5(+) CD4(+) T cell targets and disruption of T cell homeostasis that accompanies chronic immune activation.

CD4-Positive T-Lymphocytes↗

PubMed2004

IL-1 acts on antigen-presenting cells to enhance the in vivo proliferation of antigen-stimulated naive CD4 T cells via a CD28-dependent mechanism that does not involve increased expression of CD28 ligands.

The basis of the adjuvant effect of IL-1 on the clonal expansion of Ag-specific CD4 T cells was measured in vivo using the TCR transgenic T cell adoptive transfer method. Injection of Ag plus IL-1 caused naive CD4 T cells to proliferate to a greater extent than did injection of Ag alone. The T cells had to express CD28 to experience the beneficial effect of IL-1 whereas the host had to express the type I IL-1R, raising the possibility that IL-1's adjuvant properties were related to induction of CD28 ligands on APC. Surprisingly, however, expression of CD28 ligands on DC and B cells was not affected by IL-1. Therefore, the adjuvant properties of IL-1 depend on a basal level of CD28 signaling but cannot be explained by enhanced CD28 signaling due to CD28 ligand induction.

Adoptive Transfer↗

PubMed2003

Competition for self ligands restrains homeostatic proliferation of naive CD4 T cells.

T cell antigen receptor (TCR) diversity is a critical feature of adaptive immunity. However, restriction of TCR diversity is a potential risk during immune reconstitution by homeostatic proliferation. What peripheral mechanisms are in place to maintain TCR diversity during recovery from lymphopenia? Here, we examine competition between several monoclonal CD4 T cell populations in RAG(-/-) and TCR Tg RAG(-/-) environments. The results suggest that specific self ligands constitute a critical limiting resource essential for homeostatic proliferation of naive CD4 T cells. In addition, T cells ignore large numbers of competitors as long as their TCR specificity is different and other non-MHC resources are not limiting. Therefore, the numbers of self ligands expressed in the periphery set the limits on TCR diversity.

Animals↗