Human basophils and mast cells express the chemokine receptor CCR3, which binds the chemokines eotaxin and RANTES. HIV-1 Tat protein is a potent chemoattractant for basophils and lung mast cells obtained from healthy individuals seronegative for Abs to HIV-1 and HIV-2. Tat protein induced a rapid and transient Ca2+ influx in basophils and mast cells, analogous to β-chemokines. Tat protein neither induced histamine release from human basophils and mast cells nor increased IL-3-stimulated histamine secretion from basophils. The chemotactic activity of Tat protein was blocked by preincubation of FcεRI+ cells with anti-CCR3 Ab. Preincubation of Tat with a mAb anti-Tat (aa 1–86) blocked the migration induced by Tat. In contrast, a mAb specific for the basic region (aa 46–60) did not inhibit the chemotactic effect of Tat protein. Tat protein or eotaxin desensitized basophils to a subsequent challenge with the autologous or the heterologous stimulus. Preincubation of basophils with Tat protein up-regulated the level of CCR3 mRNA and the surface expression of the CCR3 receptor. Tat protein is the first identified HIV-1-encoded β-chemokine homologue that influences the directional migration of human FcεRI+ cells and the expression of surface receptor CCR3 on these cells.

Background: The aim of this study was to investigate whether human mast cells express functional active CCR3 receptors, which are activated by CC chemokines. These ligands include the CCR3-selective chemokines eotaxin and eotaxin-2 and the more promiscuous CC chemokines, MCP-4, MCP-3, MCP-2 and RANTES. Methods: Immunohistochemical analysis was performed on skin, gut and lung specimens. Double immunostaining was performed with anti-CCR3 and antitryptase, and anti-CCR3 and antichymase antibody (Ab) by using the avidin-biotin-peroxidase system with two different substrates. Mast cells were isolated and purified from human lung parenchyma (HLMC) by countercurrent elutriation followed by discontinuous Percoll density gradient. Flow-cytometric analysis of HLMC surface CCR3 expression was performed with the monoclonal Ab anti-CCR3 (7B11). Functional activation of HLMC was verified by the ability of cells to release histamine and/or migrate in response to eotaxin. Results: High percentages (>70%) of tryptase-positive cells showing CCR3 expression were found in the skin and in the intestinal submucosa, whereas much lower percentages (≤20%) were found in the intestinal mucosa and in the lung interstitium. Eotaxin (1–100 nM) neither induced histamine release from HLMC nor enhanced anti-IgE-induced histamine release. In contrast, eotaxin (10–100 nM) and RANTES (10–100 nM) induced HLMC chemotaxis in vitro. Preincubation of HLMC with antibody anti-CCR3 (5 µg/ml) before loading into the chemotaxis chamber abrogated chemotaxis elicited by eotaxin. Double immunostaining with anti-CCR3 and anti-chymase antibody showed that the vast majority of CCR3-expressing mast cells in the various human tissues examined were tryptase-chymase double-positive. Conclusions: These results indicate that CCR3 is expressed on human mast cells and that these cells are attracted by CCR3-binding chemokines.

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