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Summary Ten human melanoma cell lines (HMCL) were tested for their ability to grow subcutaneously in nude mice. Using a standard inoculum, the HMCL could be characterized by their highly, fairly or poorly xenografting phenotype. These phenotypes were stable and the phenotype of one HMCL was recovered within cell clones derived from it. The role of nude mice natural defences in the expression of HMCL xenografting phenotypes was studied. Sublethal whole body irradiation and silica pretreatment of recipients enabled poorly tumourigenic HMCL to grow in most animals without affecting their splenic NK activity. Admixture of BCG or MDP encapsulated in liposomes with highly tumourigenic HMCL resulted in the abrogation of tumour growth in naive nude mice. The long lasting abrogating of NK activity in vivo by treatment with anti-asialo-GM1 anti-serum did not enhance the growth of a poorly tumourigenic HMCL. The HMCL were found to be resistant to in vitro murine NK activity. These results showed that the expression of the HMCL xenografting phenotypes could be controlled by the nude mice natural defences. NK cells did not seem to be largely involved whereas macrophages might be good candidates as anti-xenograft effectors.

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Human rIL-4 specifically induces the expression of the low affinity receptor for IgE (Fc epsilon R2/CD23) on normal B cells and on the Burkitt lymphoma cell line Jijoye. IL-4 does not induce the generation of the second messenger cAMP in Jijoye cells. PGE2 (at 10(-7) M) was found to inhibit by 50% the IL-4 mediated Fc epsilon R2/CD23 induction on Jijoye cells. The PGE2 half maximum inhibitory concentration (1 nM) was comparable to that inducing a half maximal increase of intracellular cAMP (4nM PGE2). 8-bromo-cAMP (10(-3) M), forskolin (10(-5) M), and cholera toxin (100 ng/ml), which increase intracellular cAMP levels, also inhibited by 40 to 80% the IL-4 induced Fc epsilon R2/CD23 expression on Jijoye cells. PGE2 8-bromo-cAMP, forskolin, and cholera toxin also inhibited the IL-4-induced Fc epsilon R2/CD23 expression on normal B lymphocytes. Taken together these data suggest that PGE2 inhibits the IL-4 induced Fc epsilon R2/CD23 through an increase of intracellular cAMP. In contrast, IFN-gamma, which strongly inhibits IL-4-mediated Fc epsilon R2/CD23 expression on Jijoye cells, did not increase intracellular cAMP levels and thus probably acts through another mechanism. IFN-gamma and PGE2 did not inhibit binding of IL-4 to its receptor. It could be excluded that IFN-gamma and PGE2 were acting via an alteration/desensitization of the IL-4R inasmuch as 24 h pre-incubation of Jijoye cells with these agents affected neither the affinity of 125I-IL-4 for its receptor (Kd = 0.8 to 1.5 x 10(-10) M) nor the maximal number of binding sites per Jijoye cells (Bmax = 390 to 550). Furthermore, IFN-gamma and PGE2 did not affect the internalization and degradation of 125I-IL-4. These data demonstrate that PGE2 and IFN-gamma inhibit the IL-4-mediated induction of Fc epsilon R2/CD23 on B lymphocytes via different mechanisms that do not alter the interaction of IL-4 with its receptor.

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