Antonio de la Hera

CD3δ deficiency arrests development of the αβ but not the γδ T cell lineage

The CD3 complex found associated with the T cell receptor (TCR) is essential for signal transduction following TCR engagement. During T cell development, TCR‐mediated signalling promotes the transition from one developmental stage to the next and controls whether a thymocyte undergoes positive or negative selection. The roles of particular CD3 components in these events remain unclear. Indeed, it is unknown whether they have specialized or overlapping roles. However, the multiplicity of CD3 components and their evolutionary conservation suggest that they serve distinct functions. Here the developmental requirement for the CD3δ chain is analyzed by generating a mouse line specifically lacking this component (δ−/− mice). Strikingly, CD3δ is shown to be differentially required during development. In particular, CD3δ is not needed for steps in development mediated by pre‐TCR or γδTCR, but is required for further development of thymocytes expressing αβTCR. Absence of CD3δ specifically blocks the thymic selection processes that mediate the transition from the double‐positive to single‐positive stages of development.

Human T‐Cell Precursors: Involvement of the IL‐2 Pathway in the Generation of Mature T Cells

Despite the genetic and structural homoiogy between antigen recognition receptors expressed by both T and B cellular components of the immune system (Kronenberg et al. 1986), T-cell recognition appears to be restricted by the products of the major histocompatibility complex (MHC) (Kindred & ShrefTler 1972, Katz et al. 1973, Zinkernagei & Doherty 1974). Acquisition of MHCrestricted T-ccll function is related to the many, and yet poorly understood, selective and muturational events which take place in the thymus (Fink & Bevan 1978, von Boehmer et ai. 1978, Sprent 1978, Zinkernagel 1978, Moller 1988). Committed hematopoietic T-cell precursors colonize the thymus during ontogeny, undergo a complex developmental process leading to the expression of clonallydistributed T-cell receptors (TCR) and migrate to the periphery as immunocompetent mature T cells (Moller 1984a). Attempts in the past few years to delineate such developmental events led to the characterization of distinct thymus subpopulations by means of the ditTerential expression of various cell surface molecules. Based on phenotypic and functional criteria, further reinforced by molecular genetic approaches, increasing agreement was reached between different laboratories when trying to correlate these subsets with discrete stages of development (reviewed by Moller 1984a). Careful analyses of cell dynamics within the thymus have allowed a better appreciation of the contribution of each thymic subpopulation to the general developmental process (Scollay & Shortman 1984, Scollay et al. 1984). Although the normal rate of stem-cell seeding into the thymus is extremely low, there is an extensive and rapid

Mesenteric Th1 polarization and monocyte TNF-α production: First steps to systemic inflammation in rats with cirrhosis†

A systemic inflammatory state with increased circulating tumor necrosis factor alpha (TNF‐α) has been related to the bacterial infection susceptibility and hemodynamic derangement of patients with cirrhosis. We compared the activation status of immune cell subpopulations defined by 4‐color cytometry in mesenteric and peripheral lymph nodes and blood of rats with CCl4‐cirrhosis to define the immune response initiation site, the T‐cell and monocyte contribution to pro‐inflammatory cytokine production, as well as the pathogenic role of enteric bacteria in the cirrhosis immune response. Th1 cells and monocytes were expanded in the mesenteric nodes (P < .001) and blood (P < .001) of rats with cirrhosis, and activated to produce interferon gamma (P < .0001) and TNF‐α (P < .0001), respectively. The greater numbers of recently activated CD134+ Th cells in mesenteric nodes compared with blood, the correlation between their numbers in mesenteric nodes and blood (r = 0.66, P < .001), and the expansion of activated CD45RC− Th cells, which are unable to re‐enter lymph nodes, in mesenteric nodes but not in blood or axillary nodes points to mesenteric nodes as the origin site of activated Th cells. Abrogation of bacterial translocation by bowel decontamination reduced the number of activated Th cells and monocytes, and normalized interferon gamma production by Th cells and TNF‐α production by monocytes in mesenteric nodes and blood, respectively. In conclusion, in cirrhosis, enteric bacteria start off an orchestrated immune response cascade in mesenteric nodes involving Th1 polarization and monocyte activation to TNF‐α production. Later, the recirculation of these activated effector immune cells into blood promotes systemic inflammation. (HEPATOLOGY 2005;42:411–419.)

Two different maturational stages of natural killer lymphocytes in human newborn infants

The objective of this study was to assess the basis for the diminished natural killer (NK) lymphocyte activity of neonates. We found either severely reduced (63% of 68 neonates) or normal (similar to healthy adult) levels of NK activity. The percentages of cord blood mononuclear cells from the two groups of infants that expressed CD16, a differentiation antigen found in NK cells, were similar and within the range found in peripheral blood mononuclear cells of adults. However, infants with low NK activity had reduced numbers of cells in the CD16+56+ subpopulation, whereas the number of these effector cells present in cord blood mononuclear cells from infants with normal NK activity was within the range found in adults. Recombinant interleukin-2, but not recombinant interferon-gamma, normalized the low NK activity of infants in a dose- and time-dependent manner. Analysis of the pattern of target cell susceptibility to lysis, together with the CD16+CD3- phenotype of the precursor and effector lymphocytes, demonstrated that the induced cytotoxicity was mediated by NK cells. In contrast, NK cells from infants with normal cytotoxic levels exhibited a functional response to interleukin-2 and interferon-gamma similar to that of adults. Our results indicate that NK cells in human neonates go through two different maturational stages.

Regulation of natural killer cytotoxicity by 1,25-dihydroxyvitamin D3.

The steroid hormone 1 alpha, 25-dihydroxyvitamin D3, calcitriol, is crucial in calcium homeostasis. Calcium plays a central role in T, B, and NK cell functions, and calcitriol is a known inhibitor of T cell proliferation and immunoglobulin production. We have analyzed here the immunoregulatory effects of calcitriol on NK cell function. We show that calcitriol specifically specifically inhibits, in a time- and dose-dependent fashion, the generation of cytotoxic activity from cultured CD16+ peripheral blood NK cells. It also suppresses, at similar molar concentrations (1-10 nM), interleukin 2 (IL-2) production by PHA-activated peripheral blood lymphocytes. Calcitriol does not interfere with the cytotoxic function of NK cells, whether fresh or generated in vitro, placing the inhibition at the level of NK cell activation. Interestingly enough, exogenous IL-2 can completely reverse the suppressive effect. These findings suggest that modulation of NK cell activation by control of the internal level of IL-2 may reflect an additional paracrine calcitriol-dependent circuit with immunoregulatory consequences.

Mutual cell interactions and the selection of immune repertoires: implication in autoimmunity

Abstract The predominant neonatal lymphocyte subset - (CD5/Ly 1) + B cells and CD3 + CD4 − CD8 − T cells - can react extensively with self antigens. In this article, Miguel Marcos and colleagues point out similarities between these subsets, and postulate a role for their mutual interactions, and interactions with the conventional cell types found in adults, in the selection of mature lymphocyte repertoires and in the control of autoimmune phenomena. A disturbance in the equilibrium between these various cells may be an important factor in the development of autoimmunity.

Interleukin-2 induces cytotoxic activity in lymphocytes from regional axillary nodes of breast cancer patients.

Natural killer (NK) cells and lymphokine‐activated killer (LAK) cells have been involved in immuno‐surveillance against tumors. A normal NK activity was observed in peripheral blood (PB) mononuclear cells (MNC) from women with breast cancer, but a very low or absent NK cytotoxicity was found in the regional lymph node (RLN) MNC. However, strong cytotoxic activity against NK‐resistant and NK‐sensitive target cells can be induced in RLN MNC by long‐term (5‐day) incubation with recombinant interleukin‐2 (rIL‐2). This cytotoxic inducer effect of rIL‐2, not observed with recombinant interferon γ, was dose and time‐dependent and was not associated with modifications in the low number of Leu 11+ or Leu 7+ cells present in the population. Both the lack of NK activity and the generation of rIL‐2‐activated killer cells can be readily demonstrated in either histologically affected or unaffected RLN. These results stress the value of the immunomodulators inducing cytotoxic activity in RLN MNC of patients with tumors, and are discussed in association with their possible therapeutical role.

Human Brucellosis Is Characterized by an Intense Th1 Profile Associated with a Defective Monocyte Function

ABSTRACT In animal models, a defective Th1 response appears to be critical in the pathogenesis of brucellosis, but the Th1 response in human brucellosis patients remains partially undefined. Peripheral blood from 24 brucellosis patients was studied before and 45 days after antibiotherapy. Twenty-four sex- and age-matched healthy donors were analyzed in parallel. Significantly increased levels of interleukin 1β (IL-1β), IL-2, IL-4, IL-6, IL-12p40, gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α), but not of IL-10, in serum and/or significantly increased percentages of samples with detectable levels of these cytokines, measured by enzyme-linked immunosorbent assays (ELISA), were found for untreated brucellosis patients, but these levels were reduced and/or normalized after treatment. Flow cytometry studies showed that the intracytoplasmic expression of IFN-γ, IL-2, and TNF-α, but not that of IL-4, by phorbol myristate-activated CD4+ CD3+ and CD8+ CD3+ T lymphocytes was significantly increased in untreated brucellosis patients and was also partially normalized after antibiotherapy. The percentage of phagocytic cells, the mean phagocytic activity per cell, and the phagocytic indices for monocytes at baseline were defective and had only partially reverted at follow-up. T lymphocytes from untreated brucellosis patients are activated in vivo and show Th1 cytokine production polarization, with strikingly high serum IFN-γ levels. In spite of this Th1 environment, we found deficient effector phagocytic activity in peripheral blood monocytes.

Selective Expansion of a CD3+CD4‐CD8‐ Subpopulation in Clinical Groups Associated with Human Immunodeficiency Virus Infection

T lymphocytes (CD3+) without expression of CD4/CD8 surface antigens have recently been described in the thymus and peripheral tymphoid organs. We have conducted a retrospective analysis of the literature, seeking quantitative variations in this T‐cell subset in normal heterosexual controls, and in risk, pre‐AIDS, and AIDS groups, by means of the subtraction [CD3‐(CD4+CD8)] and the ratio 100×[CD3‐(CD4+CD8)]/CD3. Dramatic T lymphocytopaenia in AIDS patients and the progressive decay of CD4+ lymphocytes and increase of CD8+ lymphocytes throughout the clinical spectrum of HIV infection have been confirmed. Furthermore, we hereby demonstrate the selective expansion of CD3+CD4−CD8− lymphocytes, directly related to the clinical state in different clinical groups of infected people when compared with controls (P<0.05). The inverse relationship between the CD3+CD4−CD8− cell subset and other mature T‐cell subsets, mainly CD4+ (r=−0.49; P<0.01). suggests the existence of mutual regulatory interactions. These in vivo results, which are in agreement with those obtained in long‐term infected cultures, cannot be explained by direct cytopathic effects of the virus on the very few infected cells. Thus, the implication of the expansion of these functional precursors on the prognosis for infected people, and the paradoxes of the immunodeficiency, such as lymphoproliferation and autoimmune features, are discussed.