The effect of antilymphocyte globulin (ALG) on human lymphocytes in vitro: inhibition of lymphotoxin production as a sensitive indicator for ALG activity

Modulation of natural killer-mediated lysis by red blood cells

Natural killer (NK)-mediated cytotoxicity is significantly enhanced in the presence of red blood cells (RBC). The enhancement is dose dependent on the number of RBC present and can be induced by autochthonous, allogeneic, or xenogeneic RBC. The enhancement was demonstrated in cytotoxicity against two different NK-sensitive tumor target cell lines, K562 and U937, and by three different assay systems, chromium release, lactate dehydrogenase release, and inhibition of thymidine incorporation. RBC directly enhance the cytotoxic activity of NKH-1/Leu19+ large granular lymphocyte NK cells. Intact RBC have to be present during the cytotoxicity assay to induce the enhancement, which probably occurs at a postbinding, preprogramming phase. The anti-CD2 antibody Leu5 cannot block the enhancement at a concentration inhibitory to lymphocyte rosetting with sheep RBC, suggesting that the enhancement is not induced by interaction through the CD2 antigen. These results indicate that RBC are a potent modulator of NK cytotoxicity and suggest that in vitro NK studies using purified lymphocytes may not always truly reflect NK activity in the blood stream.

Normal levels of lymphotoxin secretion by freshly isolated and refrigerated human peripheral blood lymphocytes

Lymphocytes obtained by Ficoll-Hypaque density gradient centrifugation of leukocytes from 40 blood bank donors were incubated at 10(6) cells/ml for 24 h with 5 micrograms phytohemagglutinin/ml serum-free RPMI 1640 medium and secreted 34 +/- 6 U lymphotoxin/ml and 52 +/- 29 U interferon/ml. Addition of 5% fetal bovine serum (FBS) or acid-citrate-dextrose treated autologous plasma (AP) augmented lymphotoxin secretion 2-fold and interferon secretion 6-8-fold. Lymphotoxin alone was secreted in 39% of serum free cultures. Both lymphotoxin and interferon were secreted in the presence of FBS or AP. Lymphocytes refrigerated at 4 degrees C for 18 h secreted upon serum-free culture similar levels of lymphotoxin as fresh cells but cultures secreting lymphotoxin alone increased from 39 to 77%. Lymphotoxin secretion by refrigerated lymphocytes was similar in the presence or absence of FBS or AP. Interferon secretion by refrigerated lymphocytes in the presence of FBS or AP, however, increased 30-40-fold approaching levels produced by freshly isolated cells and indicating that the modulatory effects of refrigeration, FBS, and AP affected interferon not lymphotoxin secretion. The levels of lymphotoxin and interferon secreted by lymphocyte populations producing both lymphokines, furthermore, varied independently of one another providing additional evidence for the dissociability of their secretion yet possible dependence of interferon upon lymphotoxin secretion. The ability to reliably quantitate lymphotoxin secretion using refrigerated lymphocytes permits transport of lymphocytes to laboratories performing quantitative bioassay of the lymphokine. This should facilitate further evaluation of the presence and role of lymphotoxin in immunopathological and other disease states.

A comparison of the antiproliferative and antiviral activities of alpha-, beta- and gamma-interferons: description of a unified assay for comparing both effects simultaneously

An assay system is described which allows simultaneous measurement of antiviral (AV) and antiproliferative (AP) activities of various interferons (IFNs) with the same indicator cells and tests one biological function, i.e. the reduction of DNA synthesis. Human IFN-alpha, -beta, and -gamma preparations were investigated for their respective AV and AP activities. In repeated independent experiments the AP:AV ratio was found to be constant for each IFN preparation. However, striking difference in the AP:AV ratios was found between the preparations, being highest in IFN-gamma and lowest in IFN-alpha. The validity of this assay was substantiated by the observation that the AP activity of the IFNs is not influenced by virus once the cells are protected by sufficient amounts of IFN and that the score of the microscopically assessed cytopathic effect (CPE) strongly correlates with the reduction of [3H]TdR uptake in the cultures. The AP:AV ratio of a Corynebacterium parvum induced IFN resembled that of the IFN-alpha-reference, suggesting that contrary to previous reports, the C. parvum induced is of alpha type. It is suggested that the assay system presented here provides a simple means not only of comparing AP and AV ratios of various IFNs but also of characterizing IFNs of unknown type.