Interferon-induced augmentation of cytotoxic killer cell generation in mixed lymphocyte cultures: analysis of the effector cell product

Peripheral-type benzodiazepine receptor ligands modulate human natural killer cell activity

Following our earlier work, we evaluated the in vitro effect of ligands active at the peripheral-type benzodiazepine receptors on human natural killer cell activity. Peripheral blood mononuclear cells were incubated with benzodiazepine receptor ligands. After 4 h we observed a nonspecific inhibition of natural killer cell activity induced by both peripheral (Ro5-4864 and PK 11195) and central (clonazepam) benzodiazepine receptor ligands; after 24 h, the suppressive activity was specific to peripheral and mixed (diazepam) ligands, and the central-type ligand had no effect. This significant, specific suppression of NK cell activity was completely reversed by the addition of human recombinant interleukin-2 or human leukocyte interferon. Our research provides additional information on the immunomodulatory effects of peripheral-type benzodiazepine ligands. Further studies are needed to clarify the underlying mechanism of natural killer cell inhibition and to determine the clinical implications of these findings.

Modification of tumor cells by a low dose of Newcastle disease virus. III. Potentiation of tumor-specific cytolytic T cell activity via induction of interferon-alpha/beta

To investigate possibilities of augmenting tumor-specific immune responses against the highly metastatic murine lymphoma ESb, we tested the effects of the interferon inducer newcastle disease virus (NDV) or of interferon-alpha/beta as costimulator in mixed lymphocyte-tumor cell cultures (MLTC) on the tumor-specific cytolytic T cell (CTL) response. Both approaches, namely stimulation of ESb immune spleen cells with NDV-modified stimulator cells or with ESb stimulator cells and exogenous IFN-alpha/beta, led to a selective potentiation of tumor-specific CTL activity. The potent activation of tumor-specific CTL precursor (CTLP) required the simultaneous presence of the specific ESb tumor antigen--possibly to mediate a signal via the corresponding T cell receptor--and costimulators--possibly to mediate second activation signals. Increased CTL activity required only very low amounts of NDV or IFN-alpha/beta. The generation of CTL activity in the MLTC cultures could be blocked by antisera to IFN-alpha/beta, not, however by control sera. Similar effects were observed in vivo, suggesting that IFN-alpha/beta not only caused an increase in CTL activity, but was essential for the generation of CTL activity. The reduction of the generation of CTL by antiserum to IFN-alpha/beta could be overcome by excess interferon, especially when using ESb-NDV as stimulator cells.

Diminished responsiveness of male homosexual chronic hepatitis B virus carriers with HTLV-III antibodies to recombinant alpha-interferon

In a randomized controlled trial, 41 chronic hepatitis B virus carriers were allocated, by opening numbered computerized randomization envelopes, to receive recombinant interferon-alpha 2A at three different doses: 2.5; 5.0, and 10.0 mU per m2. Thirty-two patients received treatment (6 for 3 months, 26 for 6 months), and 9 patients were controls (received no treatment). Ninety-three per cent of our patients were homosexual, and 41% had anti-HTLV-III in their serum. None of the control patients lost HBeAg. In contrast, six of the anti-HTLV-III-negative patients (33%) responded to treatment (p less than 0.02): five of these responders were homosexual (p less than 0.05). The response rate was greatest (44%) in the anti-HTLV-III-negative patients who received 10 mU per m2 of recombinant interferon-alpha 2A. None of the anti-HTLV-III-positive patients responded to treatment. The percentage reduction of hepatitis B virus DNA was significantly less in the anti-HTLV-III-positive group in comparison to the anti-HTLV-III-negative group at 1 and 4 months of treatment and at 3 months after the end of treatment (p less than 0.05). These patients were younger (33 vs. 42 years, p less than 0.02), had lower mean baseline AST values (42 vs. 80 IU per liter, p less than 0.02) and tended to have milder histological disease. Homosexual men with HBeAg-positive chronic liver disease who are anti-HTLV-III-positive appear to be less responsive to the direct antiviral and immunomodulatory effects of recombinant interferon-alpha 2A. This may be due to the subclinical immunosuppressive effects of co-infection with HTLV-III.

Inhibitory effects of anti-HLA-A, B, C heavy chain and anti-beta 2 microglobulin monoclonal antibodies on alloantigen and microbial antigen-induced immune responses in vitro

The role of HLA class I subunits in class II-restricted immune responses was investigated by means of a panel of monoclonal antibodies (MoAb) recognizing HLA-A,B,C heavy chain and different beta 2 microglobulin (beta 2m) epitopes. MoAb against either class I subunit strongly inhibited mixed lymphocyte cultures, generation of cytotoxic T lymphocyte cultures, generation of cytotoxic T lymphocytes or natural killer-like activity, and lymphoproliferation in response to soluble or particulate microbial antigens derived from Candida albicans. In general, anti-beta 2m MoAb were more efficient inhibitors than anti-HLA-A,B,C heavy chain MoAb. The inhibitory effects were specific, in that the parental myeloma ascitic fluid or a low-affinity MoAb against beta 2m, or MoAb directed against non-HLA surface structures did not affect any of the immune responses studied. The MoAb-induced inhibition could not be attributed to nonspecific toxic effects, since PHA-induced blastogenesis and IL-2-dependent proliferation of mixed lymphocyte culture (MLC) blasts were not inhibited. Furthermore, exogenous IL-2 did not reverse the block of MLC and microbial antigen-induced proliferative responses by MoAb. Taken together, these data suggest an involvement of both subunits of class I antigens in class II-restricted immune responses.

Influence of monoclonal antibodies against HLA class I and class II antigen on interferon-gamma and -alpha induction

The effects of several monoclonal antibodies (MAbs) directed against different epitopes of HLA class I and class II antigens on interferon (IFN)-gamma and IFN-alpha production were studied. The results indicate that: these MAbs have a marked inhibitory effect on the production of IFN-gamma induced by alloantigens and microbial antigens; they influence only to a lesser extent staphylococcal enterotoxin B (SEB)- and phytohemagglutinin (PHA)-induced IFN-gamma production; such effects parallel inhibition of lymphoproliferation except for PHA-induced blastogenesis, which is not affected; on the other hand, these MAbs have no effect on the production of IFN-alpha induced by lipopolysaccharide (LPS) or viruses.

Action of lysosomotropic amines on spontaneous and interferon enhanced NK and CTL cytolysis

Cell-mediated cytotoxicities, such as natural killer (NK) and T-dependent cytotoxic (CTL) activities, are inhibited to the same extent by lysosomotropic amines, even when interferon is added to cultures to enhance lysis. It is postulated that the amines block steps common to spontaneous and IFN-enhanced NK and CTL lytic mechanisms.

Naturally cytotoxic tonsillar lymphocytes: a manifestation of heterogeneity among human NK cells

Lymphocytes isolated from human tonsils are capable of lysing cells of the natural killer (NK)-susceptible line K562. Although weak compared with that of autochthonous peripheral lymphocytes, cytotoxicity is invariably manifest at high effector-to-target ratios. Like peripheral NK cells, tonsillar cytotoxic lymphocytes possess a low buoyant density, which makes possible their partial enrichment from non-cytotoxic cells by centrifugation on discontinuous Percoll gradients. However, examination of cytotoxic fractions indicates that, unlike blood lymphocyte-mediated cytotoxicity, effector function is not associated with the presence of large granular lymphocytes. Furthermore, a functional distinction from classical NK cells is apparent since, although tonsillar cytotoxicity is significantly enhanced after exposure to supernatants from polyclonally activated allogeneic tonsils, pretreatment with lymphoblastoid (Namalva) interferon (IFN-alpha) at doses shown to potentiate maximally the cytotoxicity of peripheral blood lymphocytes fails to influence reactivity. These data provide preliminary evidence for the existence of, at least limited, heterogeneity among human NK cells.