Presence of soluble SLA histocompatibility antigen in pig plasma.

The major histocompatibility antigens of the pigs (SLA 1 and SLA 15) were solubilized by papain and then iodinated according to Greenwood's chloramine T method. These antigen preparations were used in radioimmunoassays for the detection of soluble inhibitors in pig plasma. Specific soluble substances were demonstrated in addition to a certain amount of cross-reactivity with other so far unidentified antigens.     

A monoclonal antibody-purified soluble target cell antigen inhibits nonspecific cytotoxic cell activity.

We have previously reported the characterization of mAb derived against NC-37 target cells. mAb 18C2 and 1E7 inhibit fish cytotoxicity by binding to target cells and thus preventing the formation of conjugates with fish nonspecific cytotoxic cells (NCC). It was therefore presumed that these inhibitory mAb were specific for the target cell Ag necessary for effector cell recognition. mAb 1D4 and 7C6 bind to NC-37 cells but do not inhibit fish cytotoxic activity. We now report the isolation and purification of the Ag recognized by mAb 18C2 (inhibitor) and 1D4 (noninhibitor) by affinity chromatography of solubilized NC-37 target cell extracts. The 18C2-purified soluble target Ag (STAg) caused inhibition of cytotoxicity when preincubated with fish NCC. This inhibitory activity was reversible and dose-dependent ranging from 20 to 70% inhibition with 25 to 100 micrograms 18C2 purified STAg/10(6) NCC. STAg purified by 1D4 affinity chromatography had no effect on fish cytotoxicity. mAb 18C2 and 1E7 preabsorbed with 18C2 STAg lost their inhibitory activity when tested in the fish NCC cytotoxicity assay. Preabsorption of the same mAb with 1D4 STAg had no effect on their activity.     

Oligomerization of soluble Fas antigen induces its cytotoxicity

Soluble Fas antigen can protect cells against Fas-mediated apoptosis. High level soluble Fas antigen characteristic for blood of patients with autoimmune disease or cancer is believed to prevent the elimination of autoimmune lymphocytes or tumor cells. Here we first report that human recombinant FasDeltaTM, i.e. soluble Fas generated by alternative splicing of the intact exon 6, is capable of inducing death of transformed cells by "reverse" apoptotic signaling via transmembrane Fas ligand. FasDeltaTM, as well as transmembrane Fas antigen, can be either monomeric or oligomeric, and both its forms are efficient in blocking Fas-mediated apoptosis, although the cytotoxic activity is exhibited solely by the latter. An in vivo analysis of soluble Fas antigen showed that unlike in healthy controls, nearly the total FasDeltaTM present in sera of rheumatoid arthritis patients was oligomeric. This resulted in suppression of cell proliferation in the experimental sera and in its promotion in controls. Thus, oligomerization/depolymerization of soluble Fas antigen can regulate its activity and contribute to the pathogenesis of autoimmune diseases and cancer.     

Enzyme activities in Schistosoma mansoni soluble egg antigen

Schistosoma mansoni egg antigens are mostly responsible for the granulomatous pathology in human intestinal schistosomiasis. Several previous studies have indicated that the induction of an immune response against some parasite enzymes may protect against pathology. The present work was designed to identify enzyme activities present in a standard soluble egg antigen (SEA) preparation. Simple colorimetric analyses were performed incubating SEA with 2-naphthyl, 2-naphthylamide (2NA), or p-nitrophenyl substrates at different pHs in the absence of added effectors. Results showed prominent acid phosphatase (pH 5.4), alkaline phosphatase (pH 8.5), and N-acetyl-beta-glucosaminidase (pH 5.4) activities. Relevant peptidase activities were also detected at pH 6.5-7.5 against 2NA derivatives of (1) aliphatic (alpha-Ala > beta-Ala > Leu > Met > S-benzyl-Cys), polar (Ser > Gln), basic (Arg > Lys > ornithine), and acidic (Glu) amino acids; (2) dipeptides: X-Ala (X = Gly > Leu > Lys > Asp), X-Arg (X = Ala > Arg > Phe > Gly > Pro > Asp), Ser-Met, and Phe-Pro; and (3) tripeptides (Ala-Phe-Pro > Phe-Pro-Ala). The data demonstrated that S. mansoni SEA contains a rich set of hydrolases with different specificities that might play a role in the egg physiology and possibly also in the host-parasite relationships.     

Characterization of Epstein-Barr virus antigens. I. Biochemical analysis of the complement-fixing soluble antigen and relationship with Epstein-Barr virus-associated nuclear antigen.

The Epstein-Barr virus-soluble (S) antigen extracted from RAJI cells was characterized by sucrose gradient centrifugation, gel filtration, and ion-exchange chromatography. The sedimentation coefficient was estimated to be 8.5S corresponding to a molecular weight of 180,000. The S antigen binds to DEAE-A25 ion exchanger from which it can be eluted with 0.3 M NaCl in Tris buffer (pH 7.2). All fractions which contained complement-fixing S antigen also inhibited the anticomplement immunofluorescence reaction as used to detect the Epstein-Barr virus-associated nuclear antigen. These results are consistent with the hypothesis that the S and Epstein-Barr virus-associated nuclear antigens are either a single antigen or that both activities are present on the same molecule.     

Systemic expression of rat soluble retinal antigen induces resistance to experimental autoimmune uveoretinitis.

To assess the role of sequestration in the maintenance of the immune privilege of the retina, retrovirally mediated gene transfer was used to express a defined, specific retinal autoantigen, rat soluble retinal Ag (S-Ag), in a systemic, nonsequestered manner. In this study we report the stable, long term transduction of rat retinal S-Ag into PBMC. Tolerance to S-Ag was assayed by challenging the S-Ag chimeric animals with S-Ag peptides in CFA and monitoring the time course and severity of experimental autoimmune uveoretinitis (EAU). The resulting data showed a correlation between the incidence of S-Ag chimerism and the loss of susceptibility to EAU. The development of resistance to EAU induction supports the hypothesis that Ag sequestration contributes to retinal immune privilege.