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PubMed1998

Activation of B cells by 1 microm particulate lysozyme or peptides: a Th-dependent pathway requiring CD40-CD40 ligand interaction.

Many antigens encountered by the immune system are included in complex structures such as bacteria or parasites. We previously developed an in vivo model to study the immunogenicity of particulate antigens, based on covalent linkage of proteins or peptides to 1 microm latex particles and showed that these antigens cannot be presented to MHC class II-restricted specific T cells by B cells. However, they induce strong CD4+ T cell responses when injected to mice without adjuvant. The present study demonstrates that four out of the five proteins tested did not stimulate antibody synthesis when linked to 1 microm microparticles, although a strong IgG production was induced by the same proteins administered in soluble form with adjuvant. In contrast, lysozyme and two synthetic peptides containing B and T cell viral epitopes induced strong and long-lasting specific antibody responses when linked to 1 micrometer synthetic beads. The isotypic pattern of antibodies induced by particulate lysozyme was similar to that induced by the soluble protein in alum. Studies using CD4+ T cell-depleted mice revealed that the induction of antibodies by particulate lysozyme strictly required Th cell activity. Moreover, the T-B cell cooperation involved in B cell activation by antigens linked to beads required CD40-CD40 ligand interaction. Thus, these particulate antigens provide a useful tool to study the mechanisms of induction of antibody response against complex bacterial or parasitic antigens. Moreover, they may represent attractive candidates to elaborate efficient new vaccines using short synthetic peptides.

Aluminum Hydroxide↗
PubMed1997

Blockade of the CD40-CD40 ligand pathway potentiates the capacity of donor-derived dendritic cell progenitors to induce long-term cardiac allograft survival.

BACKGROUND: Failure of costimulatory molecule-deficient donor dendritic cells (DCs) to induce indefinite allograft acceptance may be a result of the 'late" up-regulation of these molecules on the DCs after interaction with host T cells. Ligation of CD40 on antigen-presenting cells by its cognate ligand CD40L is thought to induce expression of CD80 (B7-1) and CD86 (B7-2). We examined the influence of anti-CD40L monoclonal antibody (mAb) on the capacity of donor-derived DC progenitors to induce long-term allograft survival. METHODS: High purity DC progenitors were grown from B10 (H2b) mouse bone marrow in granulocyte-macrophage colony-stimulating factor and transforming growth factor beta1 (TGFbeta1). Mature DC were propagated in granulocyte-macrophage colony-stimulating factor and interleukin-4. Their phenotype was characterized by flow cytometric analysis and their function by mixed leukocyte reactivity. Anti-donor cytotoxic T lymphocyte activity in grafts and spleens of vascularized heart allograft recipients was also assessed. RESULTS: The TGFbeta3-cultured cells were (1) DEC 205-positive, MHC class II-positive, CD80dim, CD86dim, and CD40dim, (2) poor stimulators of naive allogeneic T-cell proliferation, and (3) able to prolong significantly B10 cardiac allograft survival in C3H (H2k) recipients when given (2 x 10[6] i.v.) 7 days before organ transplantation (median survival time [MST] 26 days vs. 12 days in controls, and 5 days in interleukin-4 DC-treated animals). Their allostimulatory activity was further diminished by addition of anti-CD40L mAb at the start of the mixed leukocyte cultures. Anti-CD40L mAb alone (250 microg/mouse, i.p.; day -7) did not prolong cardiac graft survival (MST 12 days). In contrast, TGFbeta-cultured DCs + anti-CD40L mAb extended graft survival to a MST of 77 days, and inhibited substantially the anti-donor cytotoxic T lymphocyte activity of graft-infiltrating cells and host spleen cells assessed 8 days after transplant. CONCLUSIONS: The CD40-CD40L pathway appears important in regulation of allogeneic DC-T-cell functional interaction in vivo; its blockade increases markedly the potential of costimulatory molecule-deficient DCs of donor origin to induce long-lasting allograft survival.

Animals↗
PubMed2000

CD40-CD40 ligand-independent activation of CD8+ T cells can trigger allograft rejection.

In experimental transplantation, blockade of CD40-CD40 ligand (CD40L) interactions has proved effective at permitting long-term graft survival and has recently been approved for clinical evaluation. We show that CD4+ T cell-mediated rejection is prevented by anti-CD40L mAb therapy but that CD8+ T cells remain fully functional. Furthermore, blocking CD40L interactions has no effect on CD8+ T cell activation, proliferation, differentiation, homing to the target allograft, or cytokine production. We conclude that CD40L is not an important costimulatory molecule for CD8+ T cell activation and that following transplantation donor APC can activate recipient CD8+ T cells directly without first being primed by CD4+ T cells.

Animals↗
PubMed2000

Colitis induced by enteric bacterial antigen-specific CD4+ T cells requires CD40-CD40 ligand interactions for a sustained increase in mucosal IL-12.

C3H/HeJBir is a mouse substrain that is highly susceptible to colitis. Their CD4+ T cells react to Ags of the commensal enteric bacteria, and the latter can mediate colitis when activated by these Ags and transferred to histocompatible scid recipients. In this study, multiple long-term C3H/HeJBir CD4+ T cell (Bir) lines reactive to commensal enteric bacterial Ags have been generated. All these were Ag specific, pauciclonal, and Th1 predominant; most induced colitis uniformly after transfer to scid recipients. Lesions were focal and marked by increased expression of IL-12p40 and IFN-gamma mRNA and protein. Pathogenic Bir T cell lines expressed CD40 ligand (CD40L) when cultured with Ag-pulsed APCs in vitro. Production of IL-12 was also increased in such cultures, an effect that was Ag- and T cell-dependent and required costimulation by CD40, but not by B7. The two Bir T cell lines that did not induce lesions after transfer failed to significantly express CD40L or increase IL-12 when cultured with Ag-pulsed APCs. Administration of anti-CD40L blocked disease expression induced by pathogenic T cells. We conclude that interactions in the colon mucosa between CD40L-expressing Bir Th1 cells with APCs endogenously loaded with commensal bacterial Ags are critical for sustained increases in local IL-12 production and progression to colitis.

Adoptive Transfer↗
PubMed2001

In vivo CD40-CD154 (CD40 ligand) interaction induces integrated HIV expression by APC in an HIV-1-transgenic mouse model.

Because of their relative resistance to viral cytopathic effects, APC can provide an alternative reservoir for latently integrated HIV. We used an HIV-transgenic mouse model in which APC serve as the major source of inducible HIV expression to study mechanisms by which integrated virus can be activated in these cells. When admixed with transgenic APC, activated T lymphocytes provided a major contact-dependent stimulus for viral protein expression in vitro. Using blocking anti-CD154 mAb as well as CD154-deficient T cells, the HIV response induced by activated T lymphocytes was demonstrated to require CD40-CD154 interaction. The role of this pathway in the induction of HIV expression from APC in vivo was further studied in an experimental model involving infection of the HIV-transgenic mice with PLASMODIUM: chabaudi parasites. Enhanced viral production by dendritic cells and macrophages in infected mice was associated with up-regulated CD40 expression. More importantly, in vivo treatment with blocking anti-CD154 mAb markedly reduced viral expression in P. chabaudi-infected animals. Together, these findings indicate that immune activation of integrated HIV can be driven by the costimulatory interaction of activated T cells with APC. Because chronic T cell activation driven by coinfections as well as HIV-1 itself is a characteristic of HIV disease, this pathway may be important in sustaining viral expression from APC reservoirs.

Animals↗
PubMed2001

Coexpression of CD40 and CD40 ligand in cutaneous T-cell lymphoma (mycosis fungoides).

Microarray analysis is a promising new approach for creating specific expression profiles of multiple genes simultaneously. We quantitatively analyzed differential gene expression patterns in mycosis fungoides-derived clonal T cells and autologous, identically cultured CD4+ lymphocytes using microarrays containing 588 cDNA segments from genes relevant to cell signaling, carcinogenesis, and apoptosis. Among other dissimilarities, neoplastic T cells showed coexpression of CD40 (Bp50) and CD40 ligand (gp39, CD154). These results could be corroborated by reverse transcription-PCR, immunohistochemistry, and two-color immunofluorescence staining. Our data suggest that in cutaneous T-cell lymphoma, CD40/CD40 ligand interactions might represent a paracrine loop that is crucial not only in preventing apoptosis or positively regulating growth but also in homing of neoplastic cells to the skin.

Adult↗
PubMed1995

Immunohistologic analysis of ineffective CD40-CD40 ligand interaction in lymphoid tissues from patients with X-linked immunodeficiency with hyper-IgM. Abortive germinal center cell reaction and severe depletion of follicular dendritic cells.

The CD40 ligand (CD40L) is an activation-induced surface membrane protein expressed by CD4+ T helper cells in lymphoid follicles, and is involved in the contact-dependent signaling-mediated activation, proliferation, and differentiation of CD40+ B cells. Using immunohistochemistry, the present study analyzes the cell microenvironment of lymphoid tissues in two cases of X-linked hyper-IgM syndrome, a congenital immunodeficiency caused by mutations of the CD40L gene, and which represents a unique model to dissect the functional and morphologic consequences of disrupted CD40/CD40L interactions. Prominent primary B follicles are identified in the lymph nodes and in the extranodal lymphoid tissues from both cases, but tiny collections of Bcl-2-, MIB1/Ki67+ centroblasts are also found in one case. Despite the CD40L defect, intrafollicular CD4+CD57+ T helper cells, identified by anti-parvalbumin mAb, are normally present. However, a severe depletion of follicular dendritic cells, recognized by Abs against NGFR, CD21 and CD23, and lack of expression of the Ag recognized by KiM4p on these cells, are noticed. Finally, no major alterations of the architecture and cellular composition of the paracortical T cell area are found. A large number of plasma cells exclusively expressing IgM were detected in the colon lamina propria in one of the patients, who also had extremely elevated IgM serum levels. Taken together, these data support the idea that ineffective CD40/CD40L interactions determine both abortive germinal center cell reaction as well as severe depletion and phenotypical abnormalities of follicular dendritic cells, thus impairing the functional development of B follicles. Recurrent or persisting antigenic stimulation in mucosal tissues is likely to play a major role in determining and maintaining elevated IgM serum levels.

Adult↗
PubMed1997

Stimulation of B-chronic lymphocytic leukemia cells by murine fibroblasts, IL-4, anti-CD40 antibodies, and the soluble CD40 ligand.

Analysis of growth regulation in B-chronic lymphocytic leukemia (B-CLL) is of pivotal importance for understanding the pathophysiology and the development of new therapeutic approaches. We investigated the effect of soluble ligands and the interaction with fibroblasts in an in vitro system developed for the expansion of normal B lymphocytes. A total of 17 peripheral blood and bone marrow samples from patients with untreated B-CLL were analyzed for survival, apoptosis, and bcl-2 protein expression. The most efficient stimulus for cell survival was cocultivation with CDw32-transfected murine fibroblasts, which achieved a median of 56% surviving CD5 positive B cells with a plateau between Day 3 and Day 13 (p < 0.0001). IL-4 alone had a significant, but less profound, effect on cell survival: cell viability was increased by a factor of 1.7 on Day 3 (p = 0.001), but cell viability continued to decline. In contrast, the soluble recombinant human CD40 ligand and two different anti-CD40 antibodies did not prolong cell survival. In all experiments prolongation of cell survival was accompanied by a significant reduction of apoptosis of the leukemic B cells: in CDw32-transfected fibroblasts apoptosis was reduced by a mean of 90%, in IL-4 by a mean of 55%. Reduction in apoptotic cell death was associated with elevated bcl-2 protein levels. Our results emphasize the critical role of the interaction between B-CLL cells and CDw32-transfected fibroblasts for cell viability in vitro. Prolongation of cell survival is caused by a reduction of apoptosis and correlates with bcl-2 protein expression.

Adult↗
PubMed1995

Activated T cells induce interleukin-12 production by monocytes via CD40-CD40 ligand interaction.

Previous studies on the production of interleukin-12 (IL-12) have shown that it is released, together with other proinflammatory cytokines, shortly after exposure of phagocytic cells to a variety of pathogens. We here report that IL-12 is also released during the recall response to soluble antigen (Ag) devoid of intrinsic adjuvant activity. We show that activated T cells induce the production of IL-12 by monocytes via a mechanism involving the interaction of T cell-associated CD40 ligand with CD40 on monocytes. The data suggest that Ag presentation on monocytes favors the persistence of type 1 responses.

Antigen Presentation↗
PubMed1995

Direct physical interaction involving CD40 ligand on T cells and CD40 on B cells is required to propagate MMTV.

The propagation of mouse mammary tumor virus (MMTV) has been analyzed in mice defective for expression of CD40 ligand (CD40L). Mice with endogenous viral superantigen (SAG) delete T cells with cognate V beta independent of CD40L expression. Nevertheless, CD40L-mice do not show deletion of cognate T cells after being exposed to infectious MMTV and have greatly diminished viral replication. The response of CD40L- T cells to SAG in vitro is also impaired, but can be reconstituted by adding B cells activated by recombinant CD40L to express costimulatory molecules. Thus, direct CD40L-dependent B cell activation appears to be a critical step in the life cycle of MMTV. The initial step in SAG-dependent T cell activation, and hence the MMTV life cycle, may be mediated by non-B cells, because splenocytes from B cell-deficient SAG-transgenic mice are able to activate cognate T cells.

Animals↗
PubMed1993

In vivo CD40-gp39 interactions are essential for thymus-dependent humoral immunity. I. In vivo expression of CD40 ligand, cytokines, and antibody production delineates sites of cognate T-B cell interactions.

T-B cell interactions have a central role in the development of antibody responses. Upon activation, T helper (Th) cells express the ligand for CD40, gp39, which is essential for Th cell-dependent B cell activation. The cytokines produced by activated Th cells have a regulatory role in B cell differentiation. In this study, we investigated, using immunohistochemical techniques, the in vivo time course and localization of gp39 expression and cytokine production in relation to the specific antibody production. Both the immunization with keyhole limpet hemocyanin (KLH), a thymus-dependent (TD) antigen, and trinitrophenyl (TNP)-Ficoll, a thymus-independent type 2 (TI-2) antigen, induced Th cells to express gp39. The expression of gp39 was restricted to Th cells in the outer periarteriolar lymphocyte sheaths (outer-PALS) and around the terminal arterioles (TA). Incidentally, gp39+ Th cells were found in the corona of follicles, whereas gp39+ cells were never found in the germinal centers or marginal zones of the spleen. Maximum frequencies of gp39+ cells were observed 3 and 4 d after primary and secondary immunization with KLH. After injection of TNP-Ficoll, a marked increase in gp39+ cells was observed, confirming previous observations that activated T cells are involved in TI-2 antibody responses. Analysis of the in vivo cytokine production revealed that interleukin 2 (IL-2)-, IL-4- and interferon gamma (IFN-gamma)-producing cells (IFN-gamma-PC) developed according to similar kinetics as observed for gp39+ cells. IL-2-PC and IL-4-PC were present in higher frequencies as were IFN-gamma-PC in the immune response against TNP-KLH. Double staining experiments revealed gp39+ Th cells producing IL-2, IL-4, or IFN-gamma, suggesting that these cells were involved in both the initial activation as well as the differentiation process of B cells into antibody-forming cells. Dual immunohistochemical analysis revealed gp39+ T cells and cytokine-PC in close proximity to antigen-specific, antibody-forming B cells. In conclusion, this study shows that in vivo gp39 is expressed on activated Th cells after immunization with TD and TI-2 antigens. Furthermore, the time course and compartmentalization of gp39+ expression, cytokine production and antibody formation after immunization suggest that cognate T-B cell interactions and T cell-regulated B cell differentiation occur in the outer-PALS and around the TA of the spleen.

Animals↗
PubMed2001

Immunobiology of allograft rejection in the absence of IFN-gamma: CD8+ effector cells develop independently of CD4+ cells and CD40-CD40 ligand interactions.

Both wild-type (WT) and IFN-gamma-deficient (IFN-gamma(-/-)) C57BL/6 mice can rapidly reject BALB/c cardiac allografts. When depleted of CD8(+) cells, both WT and IFN-gamma(-/-) mice rejected their allografts, indicating that these mice share a common CD4-mediated, CD8-independent mechanism of rejection. However, when depleted of CD4(+) cells, WT mice accepted their allografts, while IFN-gamma(-/-) recipients rapidly rejected them. Hence, IFN-gamma(-/-), but not WT mice developed an unusual CD8-mediated, CD4-independent, mechanism of allograft rejection. Allograft rejection in IFN-gamma(-/-) mice was associated with intragraft accumulation of IL-4-producing cells, polymorphonuclear leukocytes, and eosinophils. Furthermore, this form of rejection was resistant to treatment with anti-CD40 ligand (CD40L) mAb, which markedly prolonged graft survival in WT mice. T cell depletion studies verified that anti-CD40L treatment failed to prevent CD8-mediated allograft rejection in IFN-gamma(-/-) mice. However, anti-CD40L treatment did prevent CD4-mediated rejection in IFN-gamma(-/-) mice, although grafts were eventually rejected when CD8(+) T cells repopulated the periphery. The IL-4 production and eosinophil influx into the graft that occurred during CD8-mediated rejection were apparently epiphenomenal, since treatment with anti-IL-4 mAb blocked intragraft accumulation of eosinophils, but did not interfere with allograft rejection. These studies demonstrate that a novel, CD8-mediated mechanism of allograft rejection, which is resistant to experimental immunosuppression, can develop when IFN-gamma is limiting. An understanding of this mechanism is confounded by its association with Th2-like immune events, which contribute unique histopathologic features to the graft but are apparently unnecessary for the process of allograft rejection.

Animals↗
PubMed1995

CD40 ligand-independent B cell activation revealed by CD40 ligand-deficient T cell clones: evidence for distinct activation requirements for antibody formation and B cell proliferation.

We report the capacity of CD40 ligand (CD40L)-negative T cell clones to activate human B cells. CD40L-negative T cells induce a level of B cell proliferation 10-20% of that seen with normal T cells. The signal provided by the negative clones is synergistic with that derived from a CD40L transfectant, and restores B cell proliferation to normal levels, showing that CD40L-negative T cell clones are not inherently inhibitory for B cells. Although their capacity to induce proliferation was much reduced, CD40L-negative T cell clones were still strong inducers of B cell differentiation to plasma cells. This differentiation to plasma cells was inhibited by a CD40L transfectant. The data are discussed with regard to the normal in vivo mechanism for maintaining B cell memory and memory antibody responses to T-dependent antigens.

Antibody Formation↗
PubMed2005

Critical function of the CD40 pathway in parvovirus B19 infection revealed by a hypomorphic CD40 ligand mutation.

Parvovirus B19-induced chronic anemia has been associated with failure to mount an effective neutralizing antibody response. We describe an adolescent male with a 13-year history of parvovirus B19-induced anemia as the primary manifestation of X-linked hyper IgM immunodeficiency (XHIM). This patient, whose serum IgG concentration was at the low end of the normal range and who mounted IgG antibody responses to T cell-dependent antigens, suffered from a nonsense mutation (R11 --> X) in the CD40 ligand (CD40L) gene. This resulted in low-level expression of a mutant CD40L predicted to lack the cytoplasmic domain. Intravenous immunoglobulin therapy alone or in combination with interferon gamma, given in the context of impaired Th1 cytokine production, suppressed but did not eradicate the infection. These results highlight the critical function of the CD40/CD40L pathway in parvovirus B19 infection and suggest that subtle defects in this pathway may underlie cases of chronic parvovirus B19 infection atypical of XHIM.

Adolescent↗
PubMed2002

Anti-lymphocyte function-associated antigen-1 monoclonal antibody inhibits CD40 ligand-independent immune responses and prevents chronic vasculopathy in CD40 ligand-deficient mice.

BACKGROUND: Blockade of CD40 ligand (CD40L; CD154, gp39) is a potential treatment for autoimmune disease and allograft rejection. However, CD40L-/- mice are capable of mobilizing cellular immune responses to viral, parasitic, and intracellular bacterial infections as well as rejecting skin grafts with nearly the same efficiency as wild-type mice. CD40L-deficient mice (CD40L-/-) or wild-type mice treated with anti-CD40L develop chronic vasculopathy only 8 weeks after allogeneic heart transplantation. To overcome CD40L-independent immune responses, we used anti-lymphocyte function-associated antigen monoclonal antibody (LFA)-1, which has previously been shown to inhibit CD8+ immune responses. METHODS: We conducted mixed lymphocyte reactions, cytotoxicity assays, skin transplantation, and vascularized heterotopic heart transplantation in wild-type B6 and CD40L-deficient mice in the presence and absence of anti-LFA-1 to study the effects of anti-LFA-1 in the absence of CD40L signaling. RESULTS: Anti-LFA-1 inhibited proliferation of naïve CD40L-/- mixed leukocyte reactions and the lysis of donor targets by CD40L-/- cytotoxic T lymphocytes. Anti-LFA-1-treated CD40L-/- mice that received fully MHC-mismatched skin grafts showed significant prolongation of graft survival, with a median survival time of 55 days (mean 66 days) compared with 13 and 21 days in wild-type and CD40L-/- controls, respectively. CD40L-/- mice that received fully MHC-mismatched vascularized heart transplants treated with four doses of 200 microg of anti-LFA-1 at the time of transplantation did not develop any signs of chronic vasculopathy 150 days after transplantation. CONCLUSION: These results indicate that anti-LFA-1 can complement CD40L inhibition in the prevention of undesirable immune responses.

Animals↗
PubMed2003

Serial measurement of surface expressions of CD63, P-selectin and CD40 ligand on platelets in atherosclerotic ischemic stroke. A possible role of CD40 ligand on platelets in atherosclerotic ischemic stroke.

BACKGROUND: Platelet activation is a key step in the progression of atherosclerosis. The CD40 ligand (CD40L) on platelets may be a critical factor to develop the acute vascular events from atheroma. METHODS: To determine the role of CD40L on platelets in atherosclerotic ischemic stroke, we serially measured the expressions of CD63, P-selectin and CD40L on platelets in patients with atherosclerotic ischemic stroke (n = 25) and compared them with those in patients with asymptomatic carotid stenosis (n = 20) and in normal subjects (n = 24). RESULTS: The expressions of CD63 and P-selectin on platelets were significantly higher in patients with atherosclerotic ischemic stroke (n = 25) than in normal subjects (n = 24). The extents of surface expressions of CD63 and P-selectin on platelets showed no significant differences between atherosclerotic ischemic stroke and asymptomatic carotid stenosis. However, the CD40L expression on platelets was significantly higher in atherosclerotic ischemic stroke when compared to that in asymptomatic carotid stenosis. CONCLUSIONS: In our data, among the population with large artery atherosclerosis, the patients with symptomatic ischemic events showed a significantly elevated expression of CD40L on platelets compared to those without ischemic events. Therefore, the upregulation of CD40L on platelets may be a specific marker of platelet activation to provoke ischemic stroke from large artery atherosclerosis.

Adult↗
PubMed2003

CD40 ligand in pathogenesis of autoimmune ovarian disease of day 3-thymectomized mice: implication for CD40 ligand antibody therapy.

The blockade of CD40 ligand (CD40L) is effective in autoimmune disease prevention. Recently, a brief period of CD40L mAb treatment was reported to induce tolerance and enhancement of CD4(+)CD25(+) regulatory T cell activity. We therefore determined the efficacy of CD40L mAb treatment in autoimmunity that resulted from CD4(+)CD25(+) regulatory T cell deficiency. Autoimmune ovarian disease (AOD) and oocyte autoantibody response of day 3-thymectomized (d3tx) mice were inhibited by continuous CD40L mAb treatment from day 3, or from days 10-14, whereas CD40L mAb treatment confined to the neonatal week was ineffective. The enhanced expression of memory markers (CD44 and CD62L(low)) on CD4(+) T cells of the d3tx mice was unaffected by CD40L mAb treatment. In contrast, their increased T cell activation markers (CD69 and CD25) were eliminated by CD40L mAb treatment. Moreover, ex vivo activated T cells of d3tx mice expressed elevated intracellular IFN-gamma, and this was also blocked by CD40L mAb. The memory T cells, although nonpathogenic in CD40L mAb-positive environment, transferred severe AOD to CD40L mAb(-) neonatal recipients. Most importantly, CD40L mAb treatment inhibited AOD in recipients of T cells from d3tx donors with severe AOD and led to regression of AOD in d3tx mice documented at 4 wk. Therefore, 1) the continuous presence of CD40L mAb both prevents and causes regression of AOD in the d3tx mice; and 2) the multiple steps of the d3tx autoimmune disease, including T cell activation, cytokine production, T cell-mediated inflammation, and tissue injury, are CD40L dependent.

Adoptive Transfer↗
PubMed2004

CD40 ligand dysregulation in HIV infection: HIV glycoprotein 120 inhibits signaling cascades upstream of CD40 ligand transcription.

IL-12 production and up-regulation of CD40 ligand (CD40L) expression are impaired in the PBMC of HIV-infected donors, and exogenous CD40L rescues IL-12 production by such cells. In this study, we implicate dysregulation of CD40L expression in the IL-12 defect associated with HIV by demonstrating that induction of CD40L expression by anti-CD3/CD28 stimulation was directly correlated with the IL-12 productive capacity of PBMC. Further, we demonstrate marked decreases in the induction of CD40L protein and mRNA following anti-CD3/CD28 stimulation in HIV-infected donors compared with uninfected donors, with a tight association between these two levels. Inhibition of CD40L up-regulation was selective, as induction of CD69 or OX40 was not as severely affected. Increased instability of CD40L mRNA did not constitute a major mechanism in CD40L dysregulation, thus suggesting a potential defect in the signaling cascades upstream of transcription. The mechanisms by which HIV infection affects the induction of CD40L expression appear to involve HIV gp120-mediated engagement of CD4. Indeed, anti-CD4 mAb or inactivated HIV virions that harbor a conformationally intact gp120 significantly inhibited CD40L up-regulation at both the protein and mRNA levels. This inhibition was due to the native, virion-associated gp120, as coculture with soluble CD4 or heat treatment of inactivated HIV abolished their effect. These in vitro models mirror the CD40L defect seen in cells from HIV-infected donors and thus provide a suitable model to investigate HIV-induced CD40L dysregulation. Clear elucidation of mechanism(s) may well lead to the development of novel immunotherapeutic approaches to HIV infection.

Adult↗