ß1 integrin is critical for the maintenance of antigen-specific CD4 T cells in the bone marrow but not long-term immunological memory.

The long-term maintenance of memory CD4 T cells promotes protective immunity against future pathogen reinfection. As a site rich in survival cytokines, the bone marrow is proposed to be a critical niche for the survival of memory CD4 T cells. We demonstrate that endogenous, polyclonal Ag-specific CD4 T cells rapidly enter and are recovered long-term from the bone marrow following i.v. infection with Listeria monocytogenes. ß(1) integrin-deficient CD4 T cells also populate the bone marrow early following an infection, but their numbers in this site rapidly decline. This decline was not caused by increased death of T cells lacking ß(1) integrin but rather by reduced retention in the bone marrow after the primary immune response. The loss of memory CD4 T cells from the bone marrow does not lead to a loss of the predominant source of memory CD4 T cells in the spleen or the ability to mount a memory response. Thus, ß(1) integrin-dependent maintenance of memory CD4 T cells in the bone marrow is not required for long-term CD4 T cell memory.

Control of alpha4beta7 integrin expression and CD4 T cell homing by the beta1 integrin subunit.

The alpha4beta7 integrin promotes homing of T cells to intestinal sites. The alpha4 integrin subunit that pairs with beta7 integrin can also pair with beta1 integrin. In this paper, we show that the preferential pairing of beta1 integrin with alpha4 integrin regulates the expression of alpha4beta7 on T cells. In the absence of beta1 integrin, naive mouse CD4 T cells have increased alpha4beta7 expression, resulting in increased adhesion to mucosal addressin cell adhesion molecule-1 and enhanced homing to Peyer's patches (PP). In a reciprocal manner, overexpression of beta1 integrin causes the loss of alpha4beta7 expression and decreased homing to PP. A similar upregulation of beta1 integrin and suppression of alpha4beta7 expression occurs rapidly after CD4 T cell activation. beta1 integrin thus dominates beta7 integrin for alpha4 integrin pairing, thereby controlling the abundance of unpaired alpha4 integrin. Increasing the abundance of alpha4 integrin relative to beta1 integrin is critical to retinoic acid-mediated expression of alpha4beta7 integrin during T cell activation. In the absence of beta1 integrin, endogenous Ag-specific CD4 T cells uniformly express high levels of alpha4beta7 after Listeria monocytogenes infection. The resulting beta1-deficient early memory T cells have decreased localization to the bone marrow and enhanced localization to PP after infection. Thus, the preferential association of beta1 integrin with alpha4 integrin suppresses alpha4beta7 integrin expression and regulates the localization of memory CD4 T cells.

Integrin function in T-cell homing to lymphoid and nonlymphoid sites: getting there and staying there.

The continuous recirculation of naive T cells and their subsequent migration to tissue following activation is crucial for maintaining protective immunity against invading pathogens. The preferential targeting of effector and memory T cells to tissue is instructed during priming and mediated by cell surface expressed adhesion receptors such as integrins. Integrins arc involved in nearly all aspects of T-cell life, including naive T-cell circulation, activation, and finally effector T-cell trafficking and localization. Recent research has revealed that microenvironmental factors present during T-cell priming result in the specific regulation of adhesion/integrin and chemokine receptor expression. Once antigen-experienced T cells enter tissue, further changes in integrin expression may occur that arc critical for T-cell localization, retention, effector function, and survival. This review discusses the function of integrin expression on T cells and the multiple roles integrins play on naive T cells and in directing effector T-cell trafficking to nonlymphoid sites in order to maintain protective adaptive immunity at body barriers.

The p110gamma isoform of phosphatidylinositol 3-kinase regulates migration of effector CD4 T lymphocytes into peripheral inflammatory sites.

The role of PI-3K in leukocyte function has been studied extensively. However, the specific role of the p110gamma isoform of PI- 3K in CD4 T lymphocyte function has yet to be defined explicitly. In this study, we report that although p110gamma does not regulate antigen-dependent CD4 T cell activation and proliferation, it plays a crucial role in regulating CD4 effector T cell migration. Naïve p110gamma(-/-) CD4 lymphocytes are phenotypically identical to their wild-type (WT) counterparts and do not exhibit any defects in TCR-mediated calcium mobilization or Erk activation. In addition, p110gamma-deficient CD4 OT.II T cells become activated and proliferate comparably with WT cells in response to antigen in vivo. Interestingly, however, antigen-experienced, p110gamma-deficient CD4 OT.II lymphocytes exhibit dramatic defects in their ability to traffic to peripheral inflammatory sites in vivo. Although antigen-activated, p110gamma-deficient CD4 T cells express P-selectin ligand, beta2 integrin, beta1 integrin, CCR4, CXCR5, and CCR7 comparably with WT cells, they exhibit impaired F-actin polarization and migration in response to stimulation ex vivo with the CCR4 ligand CCL22. These findings suggest that p110gamma regulates the migration of antigen-experienced effector CD4 T lymphocytes into inflammatory sites during adaptive immune responses in vivo.

Central type benzodiazepine receptors in Gulf War veterans with posttraumatic stress disorder.

BACKGROUND: A previous single photon emission computed tomography study showed decreased central type benzodiazepine receptors in the prefrontal cortex in Vietnam War veterans with posttraumatic stress disorder. To assess the generalizability of this finding to patients with more recent history, we studied central type benzodiazepine receptors in Gulf War veterans with posttraumatic stress disorder. METHODS: Nineteen Gulf War veterans with posttraumatic stress disorder and 19 age-matched, healthy, nondeployed veterans participated in a single photon emission computed tomography study using [(123)I]iomazenil. Regional total distribution volume (V(T)') was compared between two groups using Statistical Parametric Mapping 99 (Wellcome Department of Imaging Neuroscience, London, United Kingdom) and volumes of interest analysis. RESULTS: Benzodiazepine receptor levels did not show regional differences between the two groups, either with or without global normalization. Average difference in V(T)' was 2% across brain areas; however, by applying global normalization, V(T)' in the patient group showed significant negative correlation with childhood trauma scores in the right superior temporal gyrus. CONCLUSIONS: Less severe symptoms and shorter duration of the illness in the current group than the prior one may be the source of the difference in the results of the two studies.

Quantification of nicotinic acetylcholine receptors in human brain using [123I]5-I-A-85380 SPET.

The purpose of this study was to assess the utility of a new single-photon emission tomography ligand, [123I]5-iodo-3-[2(S)-2-azetidinylmethoxy]pyridine (5-I-A-85380), to measure regional nAChR binding in human brain. Six healthy nonsmoker subjects (two men and four women, age 33 +/- 15 years) participated in both a bolus (dose: 317 +/- 42 MBq) and a bolus plus constant infusion (dose of bolus: 98 +/- 32 MBq, B/I=6.7 +/- 2.6 h, total dose: 331 +/- 55 MBq) study. The study duration was 5-8 h and 14 h in the former and the latter, respectively. Nonlinear least-squares compartmental analysis was applied to bolus studies to calculate total (VT') and specific (VS') distribution volumes. A two-tissue compartment model was applied to identify VS'. VT' was also calculated in B/I studies. In bolus studies, VT' was well identified by both one- and two-tissue compartment models, with a coefficient of variation of less than 5% in most regions. The two-compartment model gave VT' values of 51, 22, 27, 32, 20, 19, 20, and 17 ml cm(-3) in thalamus, cerebellum, putamen, pons, and frontal, parietal, temporal, and occipital cortices, respectively. The two-compartment model did not identify VS' well. B/I studies provided poor accuracy of VT' measurement, possibly due to deviations from equilibrium conditions. These results demonstrate the feasibility of quantifying high-affinity type nAChRs using [123I]5-I-A-85380 in humans and support the use of VT' measured by bolus studies.