Immature dendritic cells (iDCs) do not mature after uptake of apoptotic cells and may play a role in the induction of peripheral tolerance to self antigens derived from apoptotic material. The integrins, αvβ3, αvβ5, and the scavenger receptor, CD36, have been shown to mediate uptake of apoptotic cells by iDCs. However, it is not known whether the complement system, also takes part in this process. In this study we investigated the ability of iDCs to bind to apoptotic cells opsonized by iC3b. Monocyte-derived dendritic cells were offered apoptotic Jurkat cells opsonized by autologous iC3b and labeled with 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanineperchlorate. A significant increase (P < 0.001) in the amount of cleared apoptotic cells was seen at low ratios. Despite increased efficiency of uptake, interaction between iC3b-opsonized apoptotic cells and iDCs down-regulated the expression of major histocompatibility complex class II, CD86, CC chemokine receptor (CCR)2, CCR5, and β2-integrins (P < 0.001), and up-regulated expression of CCR7 (P < 0.001). In addition, iDC maturation responses to CD40L and lipopolysaccharide were significantly inhibited. We conclude that opsonization of apoptotic cells by iC3b induces tolerant iDCs that are able to migrate to lymph nodes.

Approximately 50% of human breast tumors secrete a small cysteine‐rich protein, pS2, of unknown function. pS2 protein was recently found to be homologous to a porcine protein with hormonogastric activity, pancreatic spasmolytic polypeptide (PSP), in which the 5‐cysteine domain present in pS2 is tandemly duplicated. We have characterized cDNA species encoding PSP and its human and mouse counterparts, hSP and mSP. We show that hSP and pS2 are separately encoded in the genome, and that the two proteins are co‐expressed in normal stomach epithelium. However, expression of hSP was not detected in breast tumors. Computer analysis revealed that the pattern of conserved cysteine residues in hSP and pS2, the P domain, is present at the N termini of two other mammalian proteins, intestinal sucrase‐isomaltase and lysosomal alpha‐glucosidase.

The isolation and characterization of complementary DNAs (cDNAs) which code for an epithelial antigen aberrantly expressed in human breast tumor tissue are described here. The only information regarding the primary structure of this potentially important antigen has been a 20-amino-acid repeat motif. We now report the complete amino acid sequences of different forms of the human epithelial tumor antigen as deduced from the nucleotide sequence of isolated non-repeat cDNAs. The diversity of protein forms is generated by a series of alternative splicing events that occur in the regions located upstream and downstream to a central tandem repeat array. Isolated cDNAs coding for the upstream region show that differential usage of alternative splice acceptor sites may generate two protein forms containing putative signal peptides of varying hydrophobicities. The complexity of possible antigen forms is further compounded by alternative splicing events occurring in the region 3' to the repeat array. The isolated cDNAs 3' to the tandem repeats indicate that whereas one mRNA transcript is colinear with the gene, and defines an open reading frame (ORF) containing 160 amino acids downstream to the repeat array, a second cDNA correlates with a mRNA that is generated by a series of splicing events. The deduced amino acid sequence of the spliced cDNA contains an ORF that is identical for 149 amino acids downstream to the repeat array with the amino acid sequence of the unspliced cDNA. At this point it diverges and continues for an additional 179 amino acids. The sequence contains a highly hydrophobic 28-amino-acid peptide, located towards the carboxyl terminus, that may correspond to a transmembrane region. The cDNAs and deduced amino acid sequences, presented here, define the complete amino acid sequences of the epithelial tumor antigen and demonstrate the existence of multiple protein forms that probably localize to different cellular and extracellular compartments.