Expression of human endogenous retrovirus HERV-K18 superantigen is elevated in juvenile rheumatoid arthritis

OBJECTIVE

To investigate the presence of a host-encoded superantigen as possible etiologic factor in pediatric rheumatic disease. We measured the expression and the ability of interferon-alpha (IFN-alpha) to induce the human endogenous retrovirus HERV-K18 superantigen in juvenile rheumatoid arthritis (JRA) and pediatric systemic lupus erythematosus (SLE).

METHODS

Expression levels of HERV-K18 were measured in peripheral blood or synovial fluid mononuclear cells (SFMC) from 13 patients with JRA, 11 pediatric SLE patients, and 24 healthy controls, by semiquantitative reverse transcription-polymerase chain reaction, comparing 18S ribosomal transcripts as endogenous standard. IFN-alpha induction was tested by pretreatment of samples with 2000 U/ml.

RESULTS

HERV-K18 expression was significantly elevated in peripheral blood from patients with JRA (mean ratio of HERV-K18 to 18S ribosomal transcripts 2.456, SD 2.122; p = 0.014), but not patients with SLE (mean 0.997, SD 0.579; p = 0.258), compared to controls (mean 0.749, SD 0.598). HERV-K18 transcripts were detected in SFMC of 7/7 JRA patients. IFN-alpha induced HERV-K18 strongly in JRA (mean fold induction = 8.934, SD 15.556) and controls (mean 8.270, SD 6.609), but weakly in SLE (mean 2.432, SD 2.219; p = 0.009). HERV-K18 levels were found to be independent of previously determined modifiers of expression, including Epstein-Barr virus infection, IFN-alpha levels, or the percentage of B cells in peripheral blood.

CONCLUSION

HERV-K18 superantigen levels were elevated in JRA patients, but not pediatric patients with SLE, suggesting a possible mechanism for autoimmunity in the former group by superantigen stimulation of autoreactive T cells.

Antibody recognition of melphalan adducts characterized using immobilized DNA: enhanced alkylation of G-Rich regions in cells compared to in vitro

The bifunctional alkylating agent, melphalan, forms adducts on DNA that are recognized by two previously described monoclonal antibodies, MP5/73 and Amp4/42. Immunoreactivity to MP5/73 was lost when alkylated DNA was exposed to alkaline pH, while Amp4/42 only recognized the structures formed after the alkali treatment. Competitive enzyme-linked immunoadsorbent assays (ELISAs) indicated that in 0.01 and 0.1 M NaOH, loss of immunoreactivity to MP5/73 occurred with half-lives that were at least 2-fold longer than half-lives for gain of immunoreactivity to Amp4/42. This supported previously published evidence that Amp4/42 did not simply recognize all the products formed by alkali treatment of adducts that were initially recognized by MP5/73. Adducts recognized by MP5/73 on RNA were considerably more stable at 100 degrees C and pH 7 than adducts on DNA. This was consistent with the hypothesis that immunorecognition involved N7 guanine adducts and ruled out the involvement of phosphotriesters in immunoreactivity. Synthetic oligodeoxyribonucleotides, covalently immobilized onto 96-well plates, were reacted with melphalan and incubated for various periods with alkali, and then the levels of adducts recognized by each antibody in replicate wells were assayed by a direct binding ELISA. Adducts formed on oligodeoxyguanylic acid were recognized very weakly by Amp4/42, unlike other DNA sequences that were tested. Retention of immobilized DNA during alkali treatment was confirmed by immunoassay of cisplatin adducts. Poor recognition by Amp4/42 of adducts in oligodeoxyguanylic acid was confirmed by a competitive ELISA. Amp4/42, unlike MP5/73, efficiently recognized adducts resulting from alkylation of DNA with chlorambucil. It is concluded that the two antibodies recognized melphalan adducts in different DNA sequence environments and that this explains (a) the different alkali stability of immunoreactive adducts and (b) previous results which showed that, in DNA from melphalan-treated cells, adducts recognized by Amp4/42 formed a smaller proportion of total adducts compared to DNA alkylated in vitro. The results presented here indicate that this was caused by a marked cellular influence on the overall sequence-dependent pattern of DNA alkylation or repair.

Development of human anti-murine antibody (HAMA) response in patients

Human anti-mouse antibody (HAMA) response was determined in the serum of 67 patients who received subcutaneously administered radiolabelled murine monoclonal antibodies (MoAb) (50 micrograms-3 mg) for immunolymphoscintigraphy and of 10 patients with advanced colorectal cancer who received murine MoAb-N-acetyl melphalan (MoAb-N-AcMEL) conjugates (amount of MoAb ranged from 120 mg/m2 body surface area to 1000 mg/m2 body surface area) as therapy. A pre-existing low level of apparent human anti-mouse antibody reactivity could be detected in the serum of normal subjects and patients prior to administration of murine MoAb. Subcutaneous administration of low doses of murine MoAb, as used in immunolymphoscintigraphy, was associated with a low incidence (4/67 or 6%) of elevated HAMA response; the use of F(ab')2 fragments was associated with the development of elevated HAMA response in one of three patients. By contrast, therapy with hepatic artery infusion of murine MoAb-N-AcMEL conjugates in three repetitive daily doses (each infusion lasting 2 h) elicited elevated HAMA responses in 10/10 (100%) patients, usually 1-3 weeks after the start of therapy. The HAMA response of patients in the therapy group was higher than those in the immunolymphoscintigraphy study and the use of steroids did not prevent the development of the HAMA response. Further administration of MoAb-N-AcMEL conjugates to a patient, who had already developed HAMA, led to 'serum sickness'-type symptoms and a transient reduction in the HAMA titres. The elevated HAMA response was polyclonal, containing increased levels of both immunoglobulin M and G (IgM and IgG) and was directed against mouse-specific determinant, the isotype (presumed to be the Fc portion), the F(ab')2 and the 'idiotype' of mouse immunoglobulins.

[Genetic differences in mice in the sensitivity to the immunodepressive action of alkylating agents]

The immunodepressant action of cyclophosphamide, thiophosphamide and sarcolysine was examined in experimental primary immune response in mice of different lines immunized with sheep red blood cells. DBA/2 and C3H/Sn mice were marked by the highest sensitivity to the immunodepressant action of the alkylating agents. BALB/c mice were relatively resistant to the immunodepressant action. Possible reasons for the interspecific differences found are discussed.

Cell-mediated immunity and blocking factor in ovarian carcinoma

Lymphocyte-mediated cytotoxicity (cell-mediated immunity) to ovarian carcinoma cells and serum blocking factor were measured in 37 patients. Short-term cultures of tumor cells and a low ratio of effector to target cells were used throughout the study, minimizing nonspecific cytotoxicity. Sixteen patients were followed for long periods of time, and correlation with the course of the disease and with therapy could be obtained. Although the level of cell-mediated immunity did not always correspond to the clinical status of the patient, the presence of blocking factor was associated with clinical relapse in 14 of 16 patients. Chemotherapy with single alkylating agents or combinations of drugs caused no significant or permanent depression of cell-mediated immunity as measured in this way. In addition, blocking factor disappeared in 2 patients during remission. It appears that the chemotherapy for ovarian carcinoma may not be significantly immunosuppressive against established levels of cell-mediated immunity and may in certain instances have effects potentially beneficial to the host as evaluated by lymphocyte-mediated cytotoxicity and blocking factor studies.