Eosinophil leukocytes express high numbers of the chemokine receptor CCR3 which binds eotaxin, monocyte chemotactic protein (MCP)-4, and some other CC chemokines. In this paper we show that CCR3 is also highly expressed on human blood basophils, as indicated by Northern blotting and flow cytometry, and mediates mainly chemotaxis. Eotaxin and MCP-4 elicited basophil migration in vitro with similar efficacy as regulated upon activation normal T cells expressed and secreted (RANTES) and MCP-3. They also induced the release of histamine and leukotrienes in IL-3-primed basophils, but their efficacy was lower than that of MCP-1 and MCP-3, which were the most potent stimuli of exocytosis. Pretreatment of the basophils with a CCR3-blocking antibody abrogated the migration induced by eotaxin, RANTES, and by low to optimal concentrations of MCP-4, but decreased only minimally the response to MCP-3. The CCR3-blocking antibody also affected exocytosis: it abrogated histamine and leukotriene release induced by eotaxin, and partially inhibited the response to RANTES and MCP-4. In contrast, the antibody did not affect the responses induced by MCP-1, MCP-3, and macrophage inflammatory protein-1 ␣ , which may depend on CCR1 and CCR2, two additional receptors detected by Northern blotting with basophil RNA. This study demonstrates that CCR3 is the major receptor for eotaxin, RANTES, and MCP-4 in human basophils, and suggests that basophils and eosinophils, which are the characteristic effector cells of allergic inflammation, depend largely on CCR3 for migration towards different chemokines into inflamed tissues. ( J. Clin. Invest. 1997. 100:1137-1143.)

Interleukin-13 (IL-13) is a recently discovered immunoregulatory cytokine. The cellular sources of IL-13 and the regulation of its expression are largely unknown. Here we show that human basophils produce IL-13 in response to IgE-receptor (IgER) crosslinking, IL-3, IL-3 plus C5a, but not C5a alone. Human basophils express IL-13 in a restricted manner since, apart from IL-4, no other cytokines encoded on the cytokine gene cluster (IL-3, IL-5, and granulocyte macrophage-colony-stimulating factor [GM-CSF]), are induced. Highest levels of IL-13 are formed after IgE-independent activation leading to a prolonged secretion of IL-13. The response to IgER-cross-linking is more transient preferentially inducing IL-4, IL-3 is a unique cytokine regulating IL-13 production by human basophils: Among a large number of cytokines tested, only IL-3 is capable of directly inducing IL-13 expression. Furthermore, although some IL-13 is produced in response to C5a in the presence of IL-5, GM-CSF, IGF-1 or IL-1 beta, IL-3 is by far the most effective. IL-13 production was blocked by actinomycin D and cycloheximide and conditions leading to IL-13 release also lead to the induction of IL-13 mRNA. This study supports an important immunoregulatory role of human blood basophils, owing to their capacity to simultaneously express IL-13 and IL-4 in a restricted manner.

The kringle 2 (E161T/C162S/EEE[K2,,,/C169S]TT) and the kringle 3 (TYQ[K3,,]DS) domains of human plasminogen (HPg) were expressed in Eschericlzia coli in an expression vector with the phage T5 promotor/operator element N250PSN250P29 and the cDNA sequence for a hexahistidine tail to facilitate the isolation of the recombinant protein. A coagulation factor Xa (FXa)-sensitive cleavage site was introduced to remove the N-terminal histidine tag. In r-K2, mutations E161T and C162S were introduced to enhance the FXa cleavage yield and C169S to replace the cysteine residue, participating in the inter-kringle disulfide bridge between kringles 2 and 3. Recombinant proteins were isolated by affinity chromatography on Ni"-nitrilotriacetic acid/agarose and refolded under denaturing and reducing conditions followed by a non-denaturing and oxidising environment. The free thiol group in position 297 in r-K3 was selectively alkylated with iodoacetamide. The hexahistidine tail was successfully removed with FXa. The N-terminal sequence, the amino acid composition and the molecular mass analyses are in agreement with the expected data. The correct arrangement of the disulfide bonds was verified by sequence analysis of the corresponding thermolytic and subtilisin fragments. r-K2 exhibits weak binding to lysine-Bio-Gel. The weak binding affinity of r-K2 for o-aminocarboxylic acids is confirmed by intrinsic fluorescence titration with 6-aminohexanoic acid (NH,C,COOH) indicating a Kd of approximately 401 pM. In contrast, r-K3 seems to be devoid of a binding affinity for w-aminocarboxylic acids. Considering earlier determined Kd values of kringle 1, kringle 4 and kringle 5, the binding affinity of HPg kringle domains for NH,C,COOH is proposed to decrease in the following order, kringle 1 > kringle 4 > kringle 5 > kringle 2 > knngle 3.Plasminogen is the main component of the fibrinolytic system and its activated form, plasmin, is responsible for the proteolytic degradation of fibrin in blood clots. Human plasminogen (HPg) is a single-chain proenzyme of 791 amino acids. The sequence has been established by amino acid sequence analysis [l-31 and

Basophils stimulated with IL-3 plus C5a selectively express IL-4 and IL-13 and continuously produce leukotrienes (LT) for hours. C5a combined with IL-5 or granulocyte-macrophage colony-stimulated factor was, however, much less effective in promoting cytokine expression and a late continuous phase of LTC4 production, possibly due to lower expression levels of their receptor alpha chains. Basophils also express several chemoattractant receptors, including high levels of C5a receptors, macrophage chemotactic protein (MCP) receptors (CCR2) and eotaxin receptors (CCR3), intermediate levels of CXCR1, CXCR2 and platelet-activating factor receptors, and lower levels of N-formyl-Met-Leu-Phe (fMLP) receptors. However, among the corresponding agonists, only C5a, fMLP and much more weakly MCP1, were found to induce cytokine expression and continuous LTC4 release, and only when combined with IL-3. CCR3, which is highly expressed on basophils and has been shown to mediate strong migratory but weak release responses, does not regulate cytokine expression. The weakly expressed fMLP receptor is an efficient activator of several cell functions including LTC4 formation, while CXCR2 hardly affects basophil function despite considerable expression. Thus, chemoattractant-receptors mediate different cellular responses unrelated to their expression levels.

T-helper cells can differentiate into at least two subtypes secreting distinct profiles of cytokines, Th1 and Th2, regulating immunoprotection and different immunopathologies. Interleukin-4 (IL-4) is both the product and the inducer of Th2 cells, raising the question whether IL-4 can be produced in response to antigen-independent stimuli. Here we show that human basophils produce IL-4 on stimulation with IL-3 and C5a or C5adesarg in similar amounts as induced by IgE- receptor-cross-linking. C5a-induced IL-4 production requires the presence of IL-3, with little effect of the sequence of stimuli addition. No “Th1-cytokines” (interferon-gamma and IL-2) and even no “Th2-cytokines” (IL-3, IL-5, IL-10, and granulocyte-macrophage colony- stimulating factor) are produced by basophils in response to either IgE- dependent or IgE-independent activation. The generation of leukotriene C4 (LTC4) is regulated in a similar manner. However, C5a induces a rapid, transient burst of leukotriene formation only if added after IL- 3. Interestingly, upon prolonged culture, a late phase of continuous LTC4 production is observed, which also requires two signals (IL-3 and C5a), but rather depends on their continuous presence than on their sequence of action. These data describe an antigen-independent pathway of very restricted IL-4 expression. Thus, basophils must be considered as central immunoregulatory cells of the innate immune system. Furthermore, the results show that LTC4 can also be generated more continuously for many hours, a phenomenon that may be of particular importance in chornic allergic inflammation, such as asthma.