ABSTRACT
CCR5 and CXC chemokine receptor 4 (CXCR4) are coreceptors for CD4 as defined by HIV-1 glycoprotein (gp) 120 binding. Pretreatment of T cells with gp120 results in modulation of both CCR5 and CXCR4 responsiveness, which is dependent upon p56(lck) enzymatic activity. The recent findings that pretreatment of T cells with a natural CD4 ligand, IL-16, could alter cellular responsiveness to macrophage-inflammatory protein-1ss (MIP-1ss) stimulation, prompted us to investigate whether IL-16 could also alter CXCR4 signaling. These studies demonstrate that IL-16/CD4 signaling in T lymphocytes also results in loss of stromal derived factor-1alpha (SDF-1alpha)/CXCR4-induced chemotaxis; however, unlike MIP-1ss/CCR5, the effects were not reciprocal. There was no effect on eotaxin/CCR3-induced chemotaxis. Desensitization of CXCR4 by IL-16 required at least 10-15 min pretreatment; no modulation of CXCR4 expression was observed, nor was SDF-1alpha binding altered. Using murine T cell hybridomas transfected to express native or mutated forms of CD4, it was determined that IL-16/CD4 induces a p56(lck)-dependent inhibitory signal for CXCR4, which is independent of its tyrosine catalytic activity. By contrast, IL-16/CD4 desensitization of MIP-1ss/CCR5 responses requires p56(lck) enzymatic activity. IL-16/CD4 inhibition of SDF-1alpha/CXCR4 signals requires the presence of the Src homology 3 domain of p56(lck) and most likely involves activation of phosphatidylinositol-3 kinase. These studies indicate the mechanism of CXCR4 receptor desensitization induced by a natural ligand for CD4, IL-16, is distinct from the inhibitory effects induced by either gp120 or IL-16 on CCR5.
Subject(s)
CD4 Antigens/physiology , Interleukin-16/physiology , Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/metabolism , Receptors, CXCR4/antagonists & inhibitors , Receptors, CXCR4/metabolism , Animals , CD4 Antigens/metabolism , Cell Line , Cell Migration Inhibition , Chemokine CXCL12 , Chemokines, CXC/antagonists & inhibitors , Chemokines, CXC/physiology , Chemotaxis, Leukocyte/immunology , Enzyme Activation/immunology , Humans , Hybridomas , Interleukin-16/genetics , Mice , Stromal Cells/immunology , T-Lymphocytes/enzymology , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , Time Factors , src Homology Domains/immunologyABSTRACT
The ability of HIV-1 gp120 to inhibit chemokine signaling prompted us to determine whether signaling through CD4 by a natural ligand, IL-16, could alter cellular responsiveness to chemokine stimulation. These studies demonstrate that IL-16/CD4 signaling in T lymphocytes results in a selective loss of macrophage-inflammatory protein (MIP)-1 beta/CCR5-induced chemotaxis. There was no effect on monocyte chemoattractant protein-2/CCR1, -2, or -3-induced chemotaxis. Desensitization of CCR5 by IL-16 required at least 10 min of pretreatment; no modulation of CCR5 expression was observed, nor was MIP-1 beta binding to CCR5 altered. Using murine T cell hybridomas transfected to express native or mutated forms of CD4, it was determined that IL-16/CD4 induces a p56lck-dependent signal that results in desensitization of CCR5. The desensitization process is reciprocal and again selective, as prior CCR5 stimulation, but not CCR1, -2, or -3 stimulation, completely inhibits IL-16/CD4-induced T cell migration. Of interest, while p56lck enzymatic activity is not required for IL-16-induced migration, it was required for desensitization of CCR5. These studies indicate the existence of reciprocal receptor cross-desensitization between CD4 and CCR5 induced by two proinflammatory cytokines and suggest a selective relationship between the two receptors.
Subject(s)
CCR5 Receptor Antagonists , CD4 Antigens/metabolism , Immunosuppressive Agents/pharmacology , Interleukin-16/physiology , Macrophage Inflammatory Proteins/physiology , CD4 Antigens/physiology , Cells, Cultured , Chemokine CCL4 , Chemotaxis, Leukocyte/immunology , Enzyme Activation/immunology , Humans , Interleukin-16/genetics , Interleukin-16/pharmacology , Lymphocyte Specific Protein Tyrosine Kinase p56(lck)/metabolism , Receptors, CCR5/physiology , Recombinant Proteins/pharmacology , Signal Transduction/immunology , T-Lymphocytes/immunology , src Homology Domains/immunologyABSTRACT
OBJECTIVE: We have previously demonstrated that the earliest lymphocyte chemotactic factors present in bronchoalveolar lavage fluid (BALF) of subjects with atopic asthma after subsegmental antigen challenge are IL-16 and MIP-1alpha, of which IL-16 appears to contribute a majority of the chemotactic activity. Because IL-16 is released in vitro after histamine stimulation of CD8+ T cells and epithelial cells, we evaluated the potential role of histamine in the release of IL-16 into the airways of allergic asthmatics in vivo. METHODS: Eight allergic asthmatic subjects, six normal subjects, and six atopic nonasthmatic subjects were challenged with saline in the lingula and with serial concentrations of histamine (1 x 10(-7) to 5 x 10(-5) mol/L) in the right middle lobe followed by bronchoalveolar lavage (BAL) 15 minutes and 6 hours later. RESULTS: The BALF from saline- and histamine-challenged lobes of normal subjects and atopic nonasthmatic subjects contained no significant lymphocyte chemoattractant activity. In six of the eight atopic asthmatic subjects, the histamine-challenged but not saline-challenged segment contained IL-16 chemotactic activity but no other identifiable lymphocyte chemoattractant activities at 6 hours. CONCLUSIONS: IL-16 appears in the airways after histamine challenge and therefore could contribute to the earliest infiltration of CD4+ T cells and eosinophils observed after antigen challenge due to histamine release from mast cells.
Subject(s)
Asthma/immunology , Chemokines/immunology , Histamine/immunology , Interleukin-16/immunology , Lymphocytes/immunology , Adult , Asthma/pathology , Bronchial Provocation Tests , Bronchoalveolar Lavage Fluid/immunology , Chemokine CCL3 , Chemokine CCL4 , Chemokines/isolation & purification , Chemotaxis, Leukocyte/immunology , Female , Humans , Interleukin-16/isolation & purification , Lymphocytes/pathology , Macrophage Inflammatory Proteins/immunology , Macrophage Inflammatory Proteins/isolation & purification , Male , Middle AgedABSTRACT
A case of viral transmission to the father of a newly vaccinated infant shows how the virtual disappearance of a once terrifying illness can obscure its recognition and how perplexing public health issues may arise when an invaluable vaccine is anything less than perfect.