SUMMARYSecretory component (SC or polymeric immunoglobulin receptor) on mucosal epithelial cells mediates transcytosis of polymeric immunoglobulin into external fluids and functions as a receptor for polymeric immunoglobulin. SC expression in a human colonic adenocarcinoma cell line, HT-29 has been reported to be up-regulated by various cytokines, such as interferon-c, tumour necrosis factor-a and interleukin-4 (IL-4). However, up-regulation of SC by IL-1 is controversial. In this study, we investigated the effect of human recombinant IL-1 alone on SC expression in HT-29 cells in detail. Immunocytochemistry and Northern blot analysis revealed that IL-1b increased both the number of SC-positive cells and SC mRNA expression. Enzyme-linked immunosorbent assay revealed that IL-1b enhanced secretion by HT-29 cells in both time-and dose-dependent manners. IL-1a had the same effects on HT-29 cells. Northern blot analysis demonstrated that cycloheximide and actinomycin D abolished the effect of IL-1. Moreover, we detected IL-1 receptor (IL-1R) type I mRNA in HT-29 cells by polymerase chain reaction ( PCR) and sequenced the PCR-amplified product. We think that it reflects the possibility of the presence of IL-1R in HT-29 cells. From these data, we concluded that IL-1b and IL-1a play regulatory roles in SC expression, and their effects depend on de novo protein synthesis and transcription.

Joining (J) chain is a component of polymeric, but not monomeric, immunoglobulin (Ig) molecules and may play a role in their polymerization and transport across epithelial cells. To date, study of the J chain has been confined to vertebrates that produce Ig and in which the J chain displays a considerable degree of structural homology. The role of the J chain in Ig polymerization has been questioned and, since the J chain can be expressed in lymphoid cells that do not produce Ig, it is possible that the J chain may have other functions. These findings indicate that the J chain may possess functions in addition to Ig polymerization.In human ontogeny, the J chain has been detected in fetal liver at the sixth gestational week (18), and its expression was found to precede synthesis of the ,u chain at least by 1 week. Phylogenetically, the J chain has been detected in many vertebrates including fish, amphibia, reptiles, birds, and mammals, all of which produce Ig (1)(2)(3) 19). In mammals, nucleotide sequences encoding human (4), mouse (20), and bovine (21) J chains, as well as the amino acid sequences of rabbit (22) and bullfrog (23) J chains have been reported. However, expression of the J chain has not been investigated in invertebrate species in which the defense systems against foreign antigens are considerably different from those in vertebrates. Therefore, we have examined the phylogeny of J chains in various animal species, especially in invertebrates that do not produce Ig.We detected the J-chain gene in various invertebrates and compared the earthworm J-chain DNA sequence with those of mammals. The J-chain gene was detected in 12 invertebrate species but not in the sea anemone or amoeba. Furthermore, the J-chain cDNA sequence determined from earthworm RNA by reverse transcriptase (RT)-coupled PCR displayed a high degree of homology to J chains from mammals, which are known to produce Ig. These results indicate that the J chain is a primitive protein that is highly conserved in invertebrates and vertebrates. MATERIALS AND METHODSInvertebrate and Vertebrate Species and Human Cell Lines. The following invertebrate and vertebrate species were used in this study: amoeba (Acanthamoeba castellani), sea anemone

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