CD4+ murine T cell clones that express high levels of immunoglobulin binding belong to the interleukin 4-producing T helper cell type 2 subset

Human CD4(+) T-Cells: A Role for Low-Affinity Fc Receptors

Both lymphoid and myeloid cells express Fc receptors (FcRs). Low-affinity FcRs engage circulating immune complexes, which results in the cellular activation and pro-inflammatory cytokine production. FcRs participate in the internalization, transport, and/or recycling of antibodies and antigens. Cytosolic FcRs also route these proteins to proteasomes and antigen-presentation pathways. Non-activated CD4(+) T-cells do not express FcRs. Once activated, naive CD4(+) T-cells express FcγRIIIa, which, upon IC ligation, provide a costimulatory signal for the differentiation of these cells into effector cell population. FcγRIIIa present on CD4(+) T-cell membrane could internalize nucleic acid-containing ICs and elicit a cross-talk with toll-like receptors. FcγRIIIa common γ-chain forms a heterodimer with the ζ-chain of T-cell receptor complex, suggesting a synergistic role for these receptors. This review first summarizes our current understanding of FcRs on CD4(+) T-cells. Thereafter, I will attempt to correlate the findings from the recent literature on FcRs and propose a role for these receptors in modulating adaptive immune responses via TLR signaling, nucleic acid sensing, and epigenetic changes in CD4(+) T-cells.

Induced expression of FcγRIIIa (CD16a) on CD4+ T cells triggers generation of IFN-γhigh subset

Whether or not CD4(+) T-cells express low affinity receptor FcγRIIIa (CD16a) in disease pathology has not been examined in great detail. In this study, we show that a subset of activated CD4(+) T-cells in humans express FcγRIIIa. The ligation of FcγRIIIa by immune complexes (ICs) in human CD4(+) T-cells produced co-stimulatory signal like CD28 that triggered IFN-γ production. The induced expression of FcγRIIIa on CD4(+) helper T-cells is an important finding since these receptors via ITAM contribute to intracellular signaling. The induced expression of FcγRIIIa on CD4(+) T helper cells and their ability to co-stimulate T-cell activation are important and novel findings that may reveal new pathways to regulate adaptive immune responses during inflammation and in autoimmunity.

Fragments of truth: T-cell targets of polyclonal immunoglobulins in autoimmune diseases

The expanding therapeutic use of high-dose intravenous immunoglobulin (IVIg) in autoimmune diseases has raised important practical and conceptual issues over the last few years. These have prompted a number of research efforts aimed at characterizing aspects of the mechanism of action of current IVIg preparations, which might lead to the development of standardized, more cost-effective agents. Although polyclonal IgG in these preparations are mostly thought to act via direct interference with disease-specific, pathogenic autoantibodies, evidence from clinical and experimental work points to the involvement of crucial checkpoints upstream of self-reactive B-cell activation and autoantibody production. Reviewed herein are the results of the most recent studies documenting the crucial role of regulatory T cells (Treg) in the immunomodulatory activity of IVIg, and the molecular mechanisms mediating the effect of specific IgG fragments and glycoforms on Treg activity and the ensuing downregulation of T-cell effector responses of different sign and magnitude. Further progress in this area of translational research may lead to the development of innovative strategies aimed at restoring tolerance in autoimmune diseases.

Intravenous immunoglobulins promote skin allograft acceptance by triggering functional activation of CD4+Foxp3+ T cells

BACKGROUND

Intravenous immunoglobulins (IVIg) therapy is effective as a treatment for T-cell-mediated immune diseases, but whether and how IVIg suppress allogeneic T-cell responses is largely unknown.

METHODS

In vitro, human CD4(+), CD4(+)CD25(-), or CD4(+)CD25(+) T cells were stimulated with allogeneic antigen-presenting cells (APCs), and mouse CBA/Ca (H2(k)) CD4(+) or CD4(+)CD25(-) T cells were stimulated with C57BL/10 (H2(b)) splenocytes, in the presence or absence of IVIg. Proliferation, binding of IVIg, expression of activation markers, and ZAP70-phosphorylation were determined. In vivo, 1x10(5) CD4(+) or CD4(+)CD25(-) T cells of CBA/Ca mice were adoptively transferred into CBA/RAG1(-/-) mice, which were 1 day later transplanted with skin grafts of C57BL/10 mice. IVIg was administered intravenously and skin graft survival was determined.

RESULTS

IVIg bound to the surface of human and mouse CD4(+)Foxp3(+) regulatory T cells (Tregs). IVIg binding resulted in functional activation of Tregs, as detected by increased expression of surface activation markers, enhanced ZAP70-phosphorylation, and increased capacity to suppress allogeneic T-cell proliferation. IVIg inhibited allogeneic T-cell proliferation in the presence of Tregs, but this effect was abrogated on selective depletion of CD25(+) cells from responder T cells. IVIg prevented T-cell-mediated rejection of fully mismatched skin grafts in CBA/RAG1(-/-) mice reconstituted with CD4(+) T cells, but this effect was lost on selective depletion of CD4(+)CD25(+) cells from transferred T cells, indicating that IVIg induced dominant allograft protection mediated by Tregs.

CONCLUSIONS

Our data show that IVIg suppress allogeneic T-cell responses by direct activation of Tregs. IVIg treatment, which has been proven safe, may have therapeutic potential in tolerance-inducing strategies in transplant medicine.

Ig-binding receptors on human NK cells as effector and regulatory surface molecules

The receptors on human natural killer 9NK cells which can specifically bind the Fc portion of immunoglobulin molecules (Fc receptors) have been extensively studied. The best known and studied Fc receptor on human NK cells is FcgammaRIIIa. Interactions of NK cells with IgG antibodies via this receptor are well known to induce a signal transduction cascade and lead to antibody-dependent cell-mediated cytotoxicity (ADCC) as well as release of various cytokines. In addition, interactions with monomeric IgG and FcgammaRIIIa have been demonstrated, which result in negative regulation of NK activity and other immunomodulatory effects. Over the past several years, it has also become increasingly appreciated that human NK cells express a variety of other Fc receptors, including FcmuR, which also can mediate effector and immunoregulatory functions. Also, a novel form of FcgammaR has been demonstrated on human NK cells, termed FcgammaRIIc. Recent molecular studies have shown considerable polymorphism in the genes for FcgammaIIc and the functional consequences are being dissected. This appears to include cross-talk between FcgammaRIIIa and at least some forms of FcgammaRIIc, which may have important functional consequences.

Suppression of experimental autoimmune encephalomyelitis by intravenously administered polyclonal immunoglobulins

Experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats either by active immunization with myelin basic protein (MBP) or by adoptive transfer using anti-MBP specific CD4(+)T cells. Treatment with human polyclonal immunoglobulins (IgG) effectively suppressed active EAE. Time-dependent experiments demonstrated that the effect of IgG was manifested only when treatment was given immediately after immunization; administration from day 7 after disease induction did not suppress the disease. In the adoptive transfer model of EAE, IgG had no effect in vivo. However, pretreatment in vitro of the antigen-specific T-cells with IgG inhibited their ability to mediate adoptive EAE, as it did in active EAE. Similarly, in vitro IgG pretreatment of the antigen-specific T-cells suppressed the proliferative response to MBP. Fluorescent Activated Cell Sorter (FACS) analysis demonstrated the binding of IgG to activated T-cell lines that was inhibited by soluble Fc molecules. The differential effects of IgG on active EAE and on the adoptive transfer of EAE suggest that IgG in vivo can suppress disease by acting during the early phase of the immune response which involves naive T cells. The inhibition of T-cell proliferation and adoptive transfer of EAE by incubation of T cells in vitro appears to require higher concentrations of IgG than those obtained in vivo.

Rous-Whipple Award lecture. The biology and pathology of lymphocyte Fc receptors

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Balancing the immune system for tolerance: a case for regulatory CD4 cells

In the past, tolerance mechanisms have focused on processes that involve elimination (deletion) or paralysis (anergy) of immune responses. It is now becoming clearer that peripheral tolerance to antigen depends on the generation of regulatory cells that function to maintain the tolerant state. The development of peripheral tolerance may require that the immune system utilize several strategies, including deletion, anergy, and immunoregulatory pathways, and these strategies may overlap. Recent investigations using animal models of transplantation tolerance have demonstrated that immunoregulatory CD4 mechanisms may play a central role in limiting organ-destructive immune responses. In this Overview, we discuss the rationale behind the need for invoking active regulatory mechanisms in peripheral immunologic tolerance and summarize the data that support or refute a CD4 regulatory mechanism.

Potential role of Fc gamma R in early development of murine lymphoid cells: evidence for functional interaction between Fc gamma R on pre-thymocytes and an alternative, non-Ig ligand on thymic stromal cells

During early development of the murine fetal thymus a fraction of Thy+ thymocytes express Fc gamma receptors. Concurrently, a small fraction of Thy- CD44- thymocytes bind recombinant soluble Fc gamma R. These findings suggested the possibility that Fc gamma R+ pre-T cells interact with a non-Ig ligand present on fetal thymic stromal cells. Evidence in support of this concept was the finding that experimental manipulation of this putative receptor-ligand pair by anti-receptor antibody or recombinant soluble Fc gamma R influenced the developmental pattern of alpha/beta-TCR+ T cells. The restricted expression of CD16 on some pre-B cells raises the possibility that an Fc gamma R-dependent step may play a similar role in B-cell development.

An alternative Fc gamma-receptor ligand: potential role in T-cell development

Fetal pre-T cells express low-affinity receptors for IgG (Fc gamma R) at a developmental stage prior to the rearrangement and expression of immunoglobulin genes. The present studies investigated the possible functional significance of Fc gamma R on fetal pre-T cells. Between 13 and 17 days of fetal development a subpopulation of T-cell receptor-, Thy-1+ thymocytes express for gamma R. The same cells contain mRNA for several forms of Fc gamma R (Fc gamma RII beta 1, beta 2, and Fc gamma RIII). Concurrently, a Pgp-1-, Thy-1-, surface-immunoglobulin- fetal thymic cell binds recombinant soluble Fc gamma R. In principle this cell can interact with the pre-T cells through this counter-receptor. To test this possibility anti-Fc gamma RII/III antibody (2.4G2) was injected into pregnant mice and then into their offspring for 6 wk postpartum. The injected antibody induced a slight increase in the proportion of CD4 or CD8 single-positive, alpha/beta T cells in the thymus. However, in fetal thymic cultures in the presence of 2.4G2 or the recombinant soluble Fc gamma R there was an accelerated differentiation of thymocytes to single-positive, CD3-bright, heat-stable antigen-dull, alpha/beta T cells. These experiments show that Fc gamma Rs are present on pre-T cells during early fetal thymic development, and that a non-IgG ligand of the Fc gamma R is expressed concurrently on Thy- fetal thymocytes. Furthermore, the presumed interaction of Fc gamma R and the alternative ligand(s) influences T-cell development. IgG binding could be an adapted function of Fc gamma Rs, and, as shown for many members of the Ig super family, these receptors may have originally served as cell-cell recognition/interaction molecules required for hematopoietic development.

Cardiac allografts in rat recipients with simultaneous use of anti-ICAM-1 and anti-LFA-1 monoclonal antibodies leads to accelerated graft loss

Cardiac allografts from Fisher rats underwent acute rejection in Wistar King Aptekman/Hokkaido (WKAH) recipient rats. ICAM-1 molecule was induced in grafted myocytes and interstitial cells during the rejection. LFA-1 (+) inflammatory cells heavily infiltrated into rejected allografts. Monoclonal antibodies to rat ICAM-1 or LFA-1 were administered intravenously to WKAH rats receiving Fisher cardiac allografts for 3-7 consecutive days after transplantation. Anti-LFA-1 treatment for 7 consecutive days prolonged allograft survival, and two of these obtained a long-term survival. While 2 out of 13 allografts survived more than 100 days in the anti-ICAM-1-treated groups, anti-ICAM-1 treatment did not affect allograft survival in the other recipients. Surprisingly, simultaneous use of both anti-ICAM-1 and anti-LFA-1 antibodies resulted in accelerated graft loss with interstitial edema, diffuse myocardial degeneration, vascular injury and scattered hemorrhage. Thus, beneficial effects on allograft survival were partially seen when recipients were given anti-ICAM-1 or anti-LFA-1 antibody alone. However, serious disadvantage in preventing rejection was clearly seen when both anti-ICAM-1 and anti-LFA-1 antibodies were used together.

Allergen-induced CD23 on CD4+ T lymphocytes and CD21 on B lymphocytes in patients with allergic asthma: evidence and regulation

Interaction of CD4+ T cells and B cells is necessary for IgE production. It has been recently demonstrated that cell surface antigen CD21 is a ligand for CD23 (Fc epsilon RII) and that the pairing of these molecules may participate in the control of IgE production. In this study we investigated the effect of the Dermatophagoides pteronyssinus (Dpt) allergen and recombinant interleukin(rIL)-4 on the expression of CD21 and CD23 on T and B cells of asthmatic patients allergic to Dpt and of healthy controls. Peripheral blood mononuclear cells (PBMC) were incubated alone or with Dpt allergen (100 biological units/ml) and/or rIL-4 (100 U/ml) for up to 7 days. The flow-cytometric analysis of double-fluorescence staining revealed that Dpt allergen and/or rIL-4 induced CD23 on CD4+ T lymphocytes only in allergic patients. The allergen-induced CD23 on T cells is de novo synthesized antigen since no induction of CD23 on T cells was observed in cultures with 0.4 microgram/ml actinomycin D. Moreover, 100 U/ml of interferon-gamma inhibited the induction of CD23 on CD4+ T cells. T cells obtained from healthy donors did not express CD23 or CD21 antigen upon incubation with allergen and/or rIL-4. Although rIL-4 also induced CD23 in controls, the expression was only observed on CD20+ cells. The allergen alone induced a significant elevation of the mean fluorescence intensity of both CD21 and CD23 only in allergic individuals. When the cell proliferation was analyzed, a slightly increased stimulation index upon cultivation of PBMC was obtained from non-allergic donors as well, but less than in allergic patients. The co-expression of major histocompatibility complex class II molecules and CD23 on CD4+ T lymphocytes in allergic patients, as assessed by the three-color immunofluorescence analysis, indicates that these cells were activated. We conclude that CD4+ T lymphocytes possess a unique capability to express CD23 upon exposure to allergen. Moreover, the allergen-mediated induction of CD23 on T cells observed only in allergic patients may be the reason for the increase of IgE production. This would not occur in non-allergic individuals as there is no CD23 expression on T cells.

DNFB contact sensitivity (CS) in BALB/c and C3H/He mice: requirement for early-occurring, early-acting, antigen-specific, CS-initiating cells with an unusual phenotype (Thy-1+, CD5+, CD3-, CD4-, CD8-, sIg-, B220+, MHC class II-, CD23+, IL-2R-, IL-3R+, Mel-14-, Pgp-1+, J11d+, MAC-1+, LFA-1+, and Fc gamma RII+)

Immunization of mice for contact sensitivity induces two different antigen-specific Thy-1+ cell activities that are required to act in sequence for elicitation of contact sensitivity. In this study, 2,4-dinitro-1-fluorobenzene contact sensitivity responses in BALB/c and C3H/He mice demonstrated the importance of early-acting and antigen-specific contact sensitivity-initiating cells to recruit the classical, late-acting contact sensitivity effector T cells. Employing in vitro treatment of sensitized cells with monoclonal antibodies to cell surface determinants and then incubation in complement, prior to adoptive cell transfer, the contact sensitivity-initiating cells were shown to have a surface phenotype that is quite unusual for antigen-specific cells [Thy-1+, CD5+, CD3-, CD4-, CD8-, sIg-, B220+, major histocompatibility complex class II-, CD23+, IL-2R-, IL-3R+, Mel-14-, CD44+ (Pgp-1+), J11d+ (HSA+), MAC-1+, LFA-1+, and Fc gamma IIR+], and is quite different from the late-acting, contact sensitivity-effector T cells (Thy-1+, CD5+, CD3+, CD4+, CD8-, sIg-, B220-, major histocompatibility complex class II-, CD23-, IL-2R+, IL-3R-, and CD44- (Pgp-1-), J11d-(HSA-), MAC-1-, LFA-1+, Fc gamma IIR-). Contact sensitivity initiation was required for elicitation of late 24-h 2,4-dinitro-1-fluorobenzene contact sensitivity responses, in both BALB/c and C3H/He mice. Moreover, relatively high doses of some monoclonal antibodies [anti-B220 (CD45RA) and anti-CD23 (IgE Fc epsilon II receptor)] were necessary to completely eliminate all contact sensitivity-initiating cells that permitted expression of late contact sensitivity-effector T-cell activity. In contrast, high doses of monoclonal antibody specific for surface determinants of late-acting contact sensitivity effector T cells (anti-CD3 and anti-CD4), when used in high doses similar to anti-B220 and anti-CD23, had no effect on contact sensitivity-initiating cell activity. Our results indicate that two very different antigen-specific Thy-1+ cells are necessary to elicit 2,4-dinitro-1-fluorobenzene contact sensitivity in BALB/c and C3H/He mice.

Expression of the IL-1 receptor discriminates Th2 from Th1 cloned CD4+ T cells specific for Plasmodium chabaudi

The expression of selected interleukin receptors by cloned CD4+ T cells specific for the murine malaria parasite Plasmodium chabaudi chabaudi (P. chabaudi) representative of the T-helper (Th) 1 and Th2 subsets was examined. Both sets of clones expressed receptors for those interleukins for which they had a growth factor requirement in vitro. Each Th1 clone expressed receptors for, and was responsive to, interleukin (IL)-2 and IL-4, while each Th2 clone expressed receptors for, and was responsive to, IL-2, IL-4 and IL-1. IL-1 receptor (IL-1R) expression by the Th1 clones was either negligible or could not be detected. The disparity in expression of IL-1R by the Th1 and Th2 clones was more clear-cut than has been previously reported and IL-1R provided a definitive phenotypic marker for clones of the Th2 subset. Should IL-1R expression prove to be a feature of other Th2 cells cultured long-term in vitro, this will be invaluable for investigations involving the phenotyping, depletion or selection of CD4+ T cells of either Th1 or Th2 subset.

Expression of the CMRF-35 antigen, a new member of the immunoglobulin gene superfamily, is differentially regulated on leucocytes

A new monoclonal antibody, CMRF-35, has been generated that recognized a 224 amino acid cell surface protein which is a novel member of the immunoglobulin gene superfamily. The antibody, raised against large granular lymphocytes (LGL), stains LGL, monocytes, macrophages and granulocytes but not platelets or erythrocytes. In addition, a subset of peripheral blood T lymphocytes (26.6 +/- 13.4% CD5+ cells) and B lymphocytes (13.7 +/- 6.8% CD20+ cells) stained with CMRF-35 but tonsil T and B cells were essentially negative. Expression of the CMRF-35 antigen (Ag) on different leucocyte populations was markedly influenced by stimulation of the cells with mitogens and cytokines. Activation of peripheral blood T cells with phytohaemagglutinin (PHA), or phorbol myristate acetate (PMA) and calcium ionophore (CaI) led to a decrease in the proportion of CMRF-35+ T lymphocytes. In contrast, PHA activation of tonsil T lymphocytes resulted in an increase in CMRF-35 Ag expression (47.1 +/- 1.5% CD5 cells at 6 days). An increase in CMRF-35 Ag was also seen on phorbol ester and CaI-activated tonsil B cells. No change in CMRF-35 expression on natural killer (NK) cells occurred following activation with interleukin-2 (IL-2) but the CMRF-35 Ag was down-regulated following Fc receptor stimulation. A moderate increase in CMRF-35 expression occurred during monocyte-macrophage differentiation and the expression of the Ag on monocytes was differentially regulated by interferon-gamma (IFN-gamma). This regulation of the CMRF-35 Ag on the leucocyte surface suggests that the molecule has an important function common to diverse leucocyte types.

Lymphocyte Fc receptors: the special case of T cells

The different cell types of the lymphoid-myeloid lineage constitutively express various Fc receptors. The exception is the T-cell lineage where most subsets express Fc receptors only during a narrow window following cellular activation. M. Sandor and R.G. Lynch summarize information which identifies a multi-level relationship between Fc receptors and clonotypic T-cell receptors and conclude that this relationship might account for the restricted expression of Fc receptors on T cells.

Expression of IgA and IgM Fc receptors on murine T lymphocytes

Fc receptors are induced on T cells following activation via the TCR. T cells that express Fc receptors transiently have the ability to use two different cognate systems: the TCR and immunoglobulins bound to the Fc receptors. The studies discussed in this article are focused on the Fc alpha and Fc mu receptors that can be induced on certain subsets of murine T lymphocytes. The article emphasizes the role of the T cell receptor for antigen in the expression of Fc alpha and Fc mu receptors on murine T cells and reviews experimental observations that suggest significant molecular heterogeneity of these Fc receptors. The finding that regulation of expression of Fc alpha receptors and Fc mu receptors on T lymphocytes is linked to cellular activation via the CD3/TCR complex implies that these Fc receptors might mediate important functions in the biology and pathology of T cells.

Divergent immune responses to respiratory and contact chemical allergens: antibody elicited by phthalic anhydride and oxazolone

In previous studies we observed that exposure of mice to the contact allergen 2,4-dinitrochlorobenzene (DNCB) and the respiratory allergen trimellitic anhydride (TMA) resulted in qualitatively different immune responses characteristic of selective Th1- and Th2-type T helper cell activation respectively. The purpose of the present investigation was to determine whether the effects recorded with DNCB and TMA are characteristic of immune responses to contact and respiratory chemical allergens in general. Experiments have been performed with phthalic anhydride, a known human respiratory sensitizer, and with oxazolone, a potent contact allergen. Under conditions of exposure where both chemicals elicited an IgG anti-hapten antibody response, only phthalic anhydride caused an increase in the serum concentration of IgE. Furthermore, like TMA, phthalic anhydride preferentially induced IgG2b rather than IgG2a antibody. In contrast, oxazolone, like DNCB, induced a markedly stronger IgG2a than IgG2b antibody response. These data provide confirmatory evidence that chemical respiratory allergens and chemical contact allergens elicit qualitatively different immune responses which reflect their clinical effects in man.

Differential stimulation of immune function by respiratory and contact chemical allergens

The nature of immune responses induced following topical exposure to 2,4-dinitrochlorobenzene (DNCB), a potent contact allergen which lacks the capacity to cause respiratory sensitization, and trimellitic anhydride (TMA), a respiratory allergen with comparatively weak skin-sensitizing potential, have been investigated. Exposure of BALB/c strain mice to concentrations of TMA and DNCB which resulted in equivalent levels of activation (cell proliferation) in lymph nodes draining the site of application (50% TMA and 1% DNCB) induced comparable levels of contact sensitization and IgG anti-hapten antibody production. However, under these conditions, exposure only to TMA resulted in an elevation of serum IgE. Furthermore, while TMA induced IgG2b rather than IgG2a antibody the reverse pattern was observed with DNCB. These data demonstrate that TMA and DNCB elicit qualitatively different immune responses which are consistent with their potential to cause respiratory and contact allergy, respectively. The possibility that the responses induced by these chemicals reflect a differential stimulation of T-helper cell subsets (Th1 and Th2) is discussed.