ABSTRACT
IL-16 is a novel cytokine, which is chemoattractant for CD4+ T cells, macrophages, and eosinophils. Recently, it was reported that IL-16 is synthesized as an approximately 80-kDa precursor molecule, pro-IL-16. Since little is known about the processing and tissue distribution of IL-16 and pro-IL-16, we investigated the distribution of IL-16 mRNA and protein in human lymphoid tissue. Northern blotting identified IL-16 mRNA predominantly in normal lymphoid organs, including PBMC, spleen, and thymus. Immunohistochemistry of human lymph node localized IL-16 protein to lymphocyte cytoplasm within T cell zones and occasionally in lymphocytes in B cell zones. Flow cytometric detection of intracellular IL-16 showed that >70% of CD4+ and CD8+ T cells constitutively expressed IL-16 protein. Western blot analysis of PBMC revealed nearly all of this protein to be approximately 80-kDa pro-IL-16 in unstimulated PBMC, and upon cell activation, the amino terminus of pro-IL-16 is processed into multiple fragments. These results show that pro-IL-16 is widely and constitutively expressed and suggest that the amino terminus of the protein can be processed upon cell activation.
Subject(s)
Interleukin-16/metabolism , Protein Precursors/metabolism , T-Lymphocyte Subsets/metabolism , Adolescent , Adult , Amino Acid Sequence , Antibodies, Monoclonal/pharmacology , CD3 Complex/immunology , CD4-Positive T-Lymphocytes/chemistry , CD4-Positive T-Lymphocytes/immunology , CD4-Positive T-Lymphocytes/metabolism , CD8-Positive T-Lymphocytes/chemistry , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/metabolism , Humans , Interleukin-16/biosynthesis , Interleukin-16/isolation & purification , Leukocytes, Mononuclear/chemistry , Lymphocyte Activation , Molecular Sequence Data , Organ Specificity/immunology , Protein Precursors/biosynthesis , Protein Precursors/isolation & purification , Protein Processing, Post-Translational/immunology , T-Lymphocyte Subsets/chemistry , T-Lymphocyte Subsets/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.
