SummaryRecombinant monocyte chemotactic-activating factor (MCAF) has been shown to induce histamine release from human basophils with a dose response between 10 -9 and 10 -6 M. The peak of activity was reached at 10 -7 M. Histamine release by MCAF was rapid with an initial rate comparable with histamine release by an optimal dose of anti-IgE. MCAF led to peak histamine release within 1 min. 80% of the subjects tested were responsive to MCAF or anti-IgE, while all were responsive to FMLP. The percentage histamine release by MCAF was, however, less than that seen with anti-IgE or FMLP, but this was attributable to a lesser percent release in nonatopic subjects; atopic subjects responded similarly to all three agonists. MCAF was also shown to activate highly purified human basophils more readily than mixed leukocytes, and its activity was inhibited by a polyclonal rabbit antibody. At a suboptimal concentration (2.5 x 10-9 M), MCAF was unable to prime the basophil to histamine release by other secretagogues. However, interleukin 3 (I1:3) and I1:5 could each prime basophils for MCAF-induced secretion. Therefore, our results suggest that MCAF may be a major contributor to the histamine-releasing activity seen in peripheral blood mononuclear cell supernatants that has been designated histamine releasing factor(s).

Chemotaxis of different populations of cells and release of proinflammatory mediators in response to antigenic stimulation are important processes in allergic diseases. These lead to the late phase response, a hallmark of chronic allergic diseases. Recombinant RANTES, a member of the "intercrine/chemokine" family of cytokines, has been previously shown to be chemotactic for monocytes and T cells of memory/helper phenotype. In this manuscript, we show that it is capable of inducing histamine release from human basophils at concentrations as low as 10(-10) M and compare its activity with that of monocyte chemotactic and activating factor/monocyte chemoattractant protein-1 (MCAF/MCP-1), another intercrine/chemokine. RANTES (10(-7) M) caused histamine release from the leukocytes of 26 of 33 donors tested (mean 21.8 +/- 3.1%). In the same group of donors, MCAF/MCP-1, goat anti-human IgE (anti-IgE; 1 microgram/ml), and FMLP (10(-5) M) released 41.1 +/- 2.9%, 40.5 +/- 4.6%, and 44 +/- 3.1% histamine, respectively. The percent histamine release by RANTES in atopic vs nonatopics was 30.3 +/- 6.7 and 16.5 +/- 2.4, respectively (p less than 0.05), and histamine release by RANTES correlated significantly with histamine release by MCAF (r = 0.69; p less than 0.001) but not with histamine release by anti-IgE (r = 0.29; p greater than 0.05). Histamine release by RANTES and MCAF/MCP-1 was extremely rapid, reaching a maximum within 1 min. RANTES was also shown to activate highly purified basophils (80% pure), and its activity was inhibited by a polyclonal anti-RANTES antibody. At a suboptimal concentration (6 x 10(-9) M), RANTES did not prime basophils to enhance histamine release by secretagogues such as anti-IgE, C5a, or FMLP. On the other hand, preincubation of basophils with RANTES or MCAF/MCP-1 desensitized basophils to either factor but not to anti-IgE, C5a, or FMLP. Preincubation of basophils with pertussis toxin markedly diminished the basophil response to either RANTES or MCAF/MCP-1. These results suggest that RANTES and MCAF/MCP-1: 1) are potent activators of basophils; 2) may function via the same, or a closely related, receptor system in basophils; and 3) may represent a link between activation of monocytes, lymphocytes, and basophils in inflammatory disorders such as the late phase allergic reaction.

We have tested the histamine releasing properties and priming abilities of a wide range of recombinant or purified cytokines and growth factors on the basophils of 20 subjects (10 atopic and 10 nonatopic). We found that monocyte chemotactic and activating factor/monocyte chemoattractant protein-1 (MCAF/MCP-1), RANTES, human macrophage inflammatory protein-1 alpha and human inflammatory protein-1 beta, Connective tissue activating peptide III and Neutrophil Activating Peptide-2 (NAP-2) cause histamine release from basophils and are all members of the intercrine/chemokine family. MCAF/MCP-1 was as potent as anti-IgE or C5a and it is clearly the major contributor to histamine releasing factor activity. RANTES was the second major histamine releasing factor among the positive cytokines. Both MCAF/MCP-1 and RANTES are present in conditioned mononuclear cell media and can be separated using Mono Q anion exchange chromatography. We also demonstrated that RANTES has unusual chromatographic properties in spite of its isoelectric point of > 9.0 because it is largely found in peak-2 of the Mono Q column rather than peak-1 in which intercrines such as MCAF/MCP-1, IL-8, and connective tissue activating peptide III are found. All other cytokines and growth factors tested were negative, with the exception of IL-3, which caused histamine release in a subpopulation of subjects, and also primed basophils for release by anti-IgE. Other basophil primers for anti-IgE-dependent histamine release were IL-5, mast cell growth factor (c-kit ligand), and insulin-like growth factor II. Using specific neutralizing antibodies we have shown that MCAF/MCP-1, RANTES, and IL-3 contribute significantly to the activity found in mononuclear cell culture supernatants. Granulocyte-macrophage-CSF, IP-10, I-309, IL-7, IL-8, IL-9, IL-10, IL-11, IgE-binding factor, TNF-alpha, TGF-beta 1, fibroblast growth factor, epidermal growth factor, and endothelial cell growth factor were negative for direct histamine release and as primers of basophils. Our results indicate that cytokines belonging to the intercrine/chemokine family are major constituents of the activity known as "histamine releasing factor" found in MNC supernatants.

Histamine Releasing Factors have been characterized as a product of human mononuclear cells and platelets. MCAF/MCP-1, a monocyte-derived product is the most potent one described which acts rapidly (within 1 minute) upon basophils of over 90% of subjects tested. RANTES, a product of a subpopulation of CD4⁽⁺⁾ lymphocytes acts similarly but is about half as potent. CTAP III/NAP-2, by contrast, is a platelet derived HRF of low potency. It is, however, a plentiful protein and NAP-2, is derived from CTAP III by cleavage with elastase. All are members of the intercrine/chemokine group of cytokine-like molecules many of which are chemotactic factors and/or activate other cells. Interleukin 8 (NAP-1), another chemokine inhibits histamine release induced by all known forms of HRF. Interleukin 3 is a primer of basophils but at high concentrations can itself induce histamine release from a subpopulation (mainly atopic) of subjects. These proteins are thought to be important mediators of protracted inflammation and histamine release seen in allergic late phase reactions and, perhaps in specific disorders such as chronic urticaria, atopic dermatitis, scleroderma, and rheumatoid arthritis.