Interleukin-8 (IL-8) is a member of a family of pro-inflammatory cytokines. Although the best characterized activities of IL-8 include the chemoattraction and activation of neutrophils, other members of this family have a wide range of specific actions including the chemotaxis and activation of monocytes, the selective chemotaxis of memory T cells, the inhibition of hematopoietic stem cell proliferation, and the induction of neutrophil infiltration in vivo. A complementary DNA encoding the IL-8 receptor from human neutrophils has now been isolated. The amino acid sequence shows that the receptor is a member of the superfamily of receptors that couple to guanine nucleotide binding proteins (G proteins). The sequence is 29% identical to that of receptors for the other neutrophil chemoattractants, fMet-Leu-Phe and C5a. Mammalian cells transfected with the IL-8 receptor cDNA clone bind IL-8 with high affinity and respond specifically to IL-8 by transiently mobilizing calcium. The IL-8 receptor may be part of a subfamily of related G protein-coupled receptors that transduce signals for the IL-8 family of pro-inflammatory cytokines.

A human tumor necrosis factor (TNF) binding protein from serum of cancer patients was purified to homogeneity and partially sequenced. Synthetic DNA probes based on amino acid sequence information were used to isolate cDNA clones encoding a receptor for TNF. The TNF receptor (TNF-R) is a 415 amino acid polypeptide with a single membrane-spanning region. The extracellular cysteine-rich domain of the TNF-R is homologous to the nerve growth factor receptor and the B cell activation protein Bp50. Human embryonic kidney cells transfected with a TNF-R expression vector specifically bind both 125I-labeled and biotinylated TNF-alpha. Unlabeled TNF-alpha and TNF-beta were equally effective at displacing the binding of labeled TNF-alpha to TNF-R expressing cells. Northern analysis indicates a single species of mRNA for the TNF-R in a variety of cell types. Therefore, the soluble TNF binding protein found in human serum is probably proteolytically derived from the TNF-R.

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Complementary DNA clones encoding two distinct tumor necrosis factor receptors were isolated from a mouse macrophage cDNA library. The cDNA for murine tumor necrosis factor receptor type 1 (mTNF-Rl) predicts a mature polypeptide of 425 amino acids that is 64% identical to its human counterpart, whereas the cDNA of murine tumor necrosis factor receptor type 2 (mTNF-R2) predicts a mature protein of 452 amino acids that is 62% identical to human tumor necrosis factor receptor type 2. The two murine tumor necrosis factor receptors have limited sequence homology (-20% identity) in their extracellular regions but no apparent similarity in their cytoplasmic portions. Northern (RNA) analysis indicates a single 2.6-kilobase (kb) transcript for mTNF-R1;,a 3.6-kb and a more predominant 4.5-kb transcript are observed for mTNF-R2. A human cell line transfected with either mTNF-R1 or mTNF-R2 expression vectors specifically bound I-labeled recombinant murine tumor necrosis factor a (TNF-a). Although mTNF-R1 had a similar affinity for both recombinant murine TNF-a and human TNF-a, mTNF-R2 showed strong specificity for recombinant murine TNF-a. This result suggests that the various activities of human tumor necrosis factor a reported in mice or in murine cell lines are probably mediated by mTNF-R1. and 75-kDa were identified (17)(18)(19). Studies with anti-55-kDa receptor (human type 1) antibodies suggest that this receptor is involved in several TNF-mediated processes, such as cytotoxicity, resistance to chlamidiae, and synthesis of prostaglandin E2 (17, 18, 20). Although the cDNAs for both human proteins have recently been cloned (21-23), the biological activity mediated by each has yet to be demonstrated through expression of the cloned genes.Similarly, studies conducted on mouse cell lines have also suggested the presence of more than one receptor for TNF. While the reported range of Kd values for binding of recombinant murine TNF-a (mTNF-a) to a number of mouse cell lines varies only slightly, the variability in the affinity of recombinant human TNF-a (hTNF-a) binding seemed to imply that murine cells possess at least two distinct receptors (24-27). Here we describe the cloning and expression of the murine homologs of the 55-kDa and 75-kDa human TNF

The role of inhibin and activin in the initiation of follicular development, growth, and atresia was examined. Human recombinant inhibin (1 microgram) was unilaterally injected into the ovarian intrabursal space of 25-day-old rats. The contralateral ovary served as a control. Recruited growing follicles (350-500 microns) were observed 24 h after injection. The accumulation of follicles was greater in the inhibin-treated ovaries than in contralateral control ovaries. Moreover, the size distribution of the follicles was similar to the distribution of follicles recruited by systemic exogenous PMSG treatment. The effect of inhibin plus PMSG on follicular development was not different from that of PMSG treatment alone. Injection of human recombinant activin (1 microgram) into the ovarian bursa caused follicular atresia. Activin therapy blocked the follicular development caused by PMSG treatment. The effect of inhibin and activin on follicular development was further characterized by measuring the incorporation of [3H]thymidine into dividing cells. Inhibin enhanced follicular thymidine incorporation, while activin decreased granulosa cell proliferation. Furthermore, receptors for inhibin-A (6.4 x 10(3) receptors/cell) and activin-A (2.3 X 10(4) receptors/cell) were identified on granulosa cells. The evidence suggests that inhibin and activin act in a paracrine manner to regulate follicular development, inhibin as a follicular growth signal and activin as an atretagenic signal.