Monoclonal antibodies to hemagglutinin and to H-2 inhibit the cross-reactive cytotoxic T cell populations induced by influenza

Influenza virus hemagglutinin-specific cytotoxic T cell response induced by polypeptide produced in Escherichia coli

We have tested the abilities of various polypeptides of A/PR/8/34 (H1N1) virus, constructed by recombinant DNA techniques, to induce influenza virus-specific secondary cytotoxic T lymphocyte (CTL) responses. A hybrid protein (c13 protein), consisting of the first 81 amino acids of viral nonstructural protein (NS1) and the HA2 subunit of viral hemagglutinin (HA), induced H-2-restricted, influenza virus subtype-specific secondary CTL in vitro, although other peptides did not. Using a recombinant virus, the viral determinant responsible for recognition was mapped to the HA2 portion of c13 protein. Immunization of mice with c13 protein induced the generation of memory CTL in vivo. The CTL precursor frequencies of A/PR/8/34 virus- and c13 protein-immune mice were estimated as one in 8,047 and 50,312, respectively. These results indicate that c13 protein primed recipient mice, even though the level of precursor frequency was below that observed in virus-immune mice.

Influenza virus M2 protein is an integral membrane protein expressed on the infected-cell surface

The influenza A virus M2 protein is expressed abundantly at the cell surface, and in addition to the hemagglutinin (HA) and neuraminidase (NA), is a third virus-specific membrane protein. M2 has an internal hydrophobic membrane anchorage domain and associates with the same cellular membrane fractions as HA and NA. Trypsin treatment of infected cells and immunoprecipitation with site-specific antisera indicate that a minimum of 18 NH2-terminal amino acids of M2 are exposed at the cell surface. Ten NH2-terminal residues are conserved in all strains of influenza A virus for which sequences are available. Antibodies can recognize M2 on the cell surface and therefore it may be an infected-cell surface antigen. We discuss properties of M2 that match it to the elusive major target molecule on influenza A virus-infected cells for cross-reactive cytotoxic T cells.

Hypothesis: the MHC-restricted T-cell receptor as a structure with two multistate allosteric combining sites

This paper presents a dual-recognition model of the T-cell receptor that has been constructed to account for the phenomenon of MHC restriction as well as the paradoxical ability of T-cells to be both multispecific and precisely specific at the same time. In our model the combining sites for antigen and MHC are not independent as in classical dual-recognition models, but interact with each other by an allosteric mechanism. We envision a flexible receptor with combining sites for antigen and MHC that are capable of existing in a multitude of distinct complementarity states. MHC and antigen molecules act as allosteric effectors such that one ligand perturbs the conformation and therefore the specificity of the site for the other ligand. An essential feature of the model is that different MHC determinants induce different conformations at the anti-antigen site. In this way the receptor acquires multiple specificities. Within a particular complementarity state, precise recognition results from the requirement that antigen and MHC exhibit positive cooperativity in their binding to the T-cell receptor. Positive cooperativity is also the basis for MHC restriction. Reaction mechanisms are presented which describe the requirement that antigen and MHC both induce conformational changes in order to generate high-affinity binding to either ligand. As a precedent for the multistate allosteric receptor model, we discuss the properties of allosteric enzymes, especially ribonucleotide reductase, whose properties are analogous to those we have postulated for the T-cell receptor. Also discussed is the possibility that molecules such as Ly2, L3T4 and the Mls antigen, which have been found to play a role in antigen recognition, function as affinity-enhancing allosteric effectors that interact with the constant portion of the T-cell receptor.

The influenza A virus nucleoprotein gene controls the induction of both subtype specific and cross-reactive cytotoxic T cells

Using genetically typed recombinant influenza A viruses that differ only in their genes for nucleoprotein, we have demonstrated that repeated stimulation in vitro of C57BL/6 spleen cells primed in vivo with E61-13-H17 (H3N2) virus results in the selection of a population of cytotoxic T lymphocytes (CTL) whose recognition of infected target cells maps to the gene for nucleoprotein of the 1968 virus. Influenza A viruses isolated between 1934 and 1979 fall into two groups defined by their ability to sensitize target cells for lysis by these CTL: 1934-1943 form one group (A/PR/8/34 related) and 1946-1979 form the second group (A/HK/8/68 related). These findings complement and extend our previous results with an isolated CTL clone with specificity for the 1934 nucleoprotein (27, 28). It is also shown that the same spleen cells derived from mice primed with E61-13-H17 virus in vivo, but maintained in identical conditions by stimulation with X31 virus (which differs from the former only in the origin of its gene for NP) in vitro, results in the selection of CTL that cross-react on target cells infected with A/PR/8/1934 (H1N1) or A/Aichi/1968 (H3N2). These results show that the influenza A virus gene for NP can play a role in selecting CTL with different specificities and implicate the NP molecule as a candidate for a target structure recognized by both subtype-directed and cross-reactive influenza A-specific cytotoxic T cells.

Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

The immunological surveillance hypothesis was formulated prior to the realization of the fact that an individual's effector T cells generally only see neoantigen if it is appropriately presented in the context of self MHC glycoproteins. The biological consequence of this mechanism is that T lymphocytes are focused onto modified cell-surface rather than onto free antigen. The discovery of MHC-restricted T cell recognition, and the realization that T cell-mediated immunity is of prime importance in promoting recovery from infectious processes, has thus changed the whole emphasis of the surveillance argument. Though the immunological surveillance hypothesis generated considerable discussion and many good experiments, there is no point in continuing the debate in the intellectual context that seemed reasonable in 1970. It is now much more sensible to think of "natural surveillance" and "T cell surveillance," without excluding the probability that these two systems have elements in common. We can now see that T cell surveillance probably operates well in some situations, but is quite ineffective in many others. Part of the reason for this may be that the host response selects tumor clones that are modified so as to be no longer recognized by cytotoxic T cells. The possibility that this reflects changes in MHC phenotype has been investigated, and found to be the case, for some experimental tumors. In this regard, it is worth remembering that many "mutations" in MHC genes that completely change the spectrum of T cell recognition are serologically silent. The availability of molecular probes for investigating the status of MHC genes in tumor cells, together with the capacity to develop cloned T cell lines, monoclonal antibodies to putative tumor antigens, and cell lines transfected with genes coding for these molecules, indicates how T cell surveillance may profitably be explored further in both experimental and human situations.

Loss of serological determinants does not affect recognition of H-2Kk target cells by an influenza-specific cytotoxic T cell clone

The recognition of "self determinants" by an H-2Kk-restricted cytotoxic T (Tc) cell clone (K5) has been investigated as follows: (a) differential inhibition of cytotoxicity by several monoclonal antibodies directed to determinants on the H-2Kk molecule of the target cells and (b) recognition and lysis of target cell variants of cell line LDHB, which have lost the majority or all of the serological determinants defined by the inhibiting antibodies while still expressing an H-2Kk molecule. Such variant cells infected with influenza virus were effectively recognized by Tc cell clone K5, whereas a target cell line, which lacks the Kk molecule, was not lysed. The results suggest; (a) that virus-specific Tc cell see "self" in a manner distinct from the recognition of serological determinants by B cell and (b) that antibody inhibition indicates conformational closeness, but not identity, of the class I determinant seen by T cells.

Intratypic and intertypic specificity of lymphocytes involved in the recognition of herpes simplex virus glycoproteins

Cytotoxic T lymphocytes (CTL) were generated in C57BL/6 mice with herpes simplex virus type 1 (HSV-1) (strains KOS, 17, HFEM, and mP) and HSV-2 (strains 186, G, and GP6). Effector lymphocytes were tested for cytotoxicity against syngeneic HSV-1- and HSV-2-infected cells in a 5-h 51Cr release assay. HSV-1 strain HFEM was found to induce CTL efficiently only when 100-fold more virus was used as compared with HSV-1 strains KOS, 17, and mP. All HSV-1 and HSV-2 strains induced cross-reactive populations of CTL. CTL generated by HSV-1 KOS and HSV-2 186 also demonstrated cross-reactivity in an ear-swelling model for delayed-type hypersensitivity. Lymphocytes generated by all HSV-2 strains were highly efficient at lysing HSV-1-infected target cells. However, HSV-2-infected target cells were found to be less susceptible to lysis by either HSV-1 or HSV-2 CTL than were HSV-1-infected target cells. The lowered susceptibility of HSV-2-infected cells was not due to an inefficient infection of BL/6 WT-3 cells as measured by standard growth assays and infectious center assays. Varying the multiplicity of infection or the time of infection did not increase the susceptibility of HSV-2-infected target cells to lysis by CTL. Increasing the effector-to-target-cell ratio resulted in an increased lysis of both HSV-1- and HSV-2-infected target cells by CTL, but the level of HSV-2-infected target cell lysis still did not approach the level of HSV-1-infected target cell lysis. HSV-2-infected cells were as efficient as HSV-1-infected cells in the cold cell competition assay employed in reducing the lysis of 51Cr-labeled, HSV-1-infected target cells. In addition, HSV-2-infected cells were susceptible to lysis by HSV-immune serum and complement.

Monoclonal antibodies to Epstein-Barr virus-induced, transformation-associated cell surface antigens: binding patterns and effect upon virus-specific T-cell cytotoxicity

Spleen cells from mice immunized with Epstein-Barr virus-transformed lymphoblastoid cells (EB-LCL) were used to generate monoclonal antibodies to cell surface antigens associated with the EB virus-transformed state. Radioimmune and immunofluorescence binding assays identified two antibodies, MHM6 and AC2, which reacted consistently with all EB-LCL tested, with a subpopulation of cells in some but not all EB virus genome-positive Burkitt lymphoma lines, but with none of a range of EB virus genome-negative cell lines of lymphoma or leukaemia origin. While MHM6 appeared to bind an EB virus-related antigen, AC2 bound some other cell surface antigen which was also found on a small subpopulation of cells in lymphocyte cultures stimulated with phytohaemagglutinin or with pokeweed mitogen. MHM6 and AC2 recognized single polypeptides with apparent molecular weights of 45 kd and 80 kd respectively as shown by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 125I-labeled cell surface polypeptides immunoprecipitated with these antibodies. These polypeptides were induced on experimentally-infected B cells within 24 h of the expression of the EB virus nuclear antigen, EBNA, at a time known to coincide with the appearance of the lymphocyte-detected membrane antigen, LYDMA. However, saturating concentration of MHM6 and AC2 were unable to protect EB-LCL target cells from lysis by LYDMA-specific cytotoxic T cells in a chromium-release assay.

Modification of cytotoxic T-cell response patterns by administration of hemagglutinin-specific monoclonal antibodies to mice infected with influenza A viruses

Mice injected with any influenza A virus develop a range of virus-immune cytotoxic T lymphocytes, some of which tend to be more lytic for cells expressing the virus used for priming (subtype-specific) while others are cross-reactive for targets infected with all influenza A viruses. Treatment with large doses of either of two monoclonal antibodies (which bind to the influenza virus hemagglutinin molecule) at 3-48 h after exposure to virus tends to selectively block the generation of the more subtype-specific cytotoxic T lymphocyte subset, although the magnitude of cross-reactive effector function may also be diminished. Inhibition that is less obviously selective is also seen for a third monoclonal antibody. A reasonable explanation for these findings is that there is afferent blockage at the level of T-cell recognition of the influenza virus hemagglutinin molecule expressed on stimulator cells. The inhibitory effect of the monoclonal antibody is apparently steric. Priming with parental strain virus followed by exposure to monoclonal antibody induces a population of cytotoxic T lymphocytes which manifest decreased cytotoxic activity for target cells infected with either the parental strain virus or with a variant virus to which the monoclonal antibody does not bind. A more practical consideration is that the administration of large doses of specific immunoglobulin may interfere with the development of cell-mediated immune mechanisms. This should be considered when developing possible therapeutic protocols using monoclonal antibodies.

Cytotoxic T cell recognition of Epstein-Barr virus-infected B cells. II. Blocking studies with monoclonal antibodies to HLA determinants

Monoclonal antibodies specifically binding common determinants on all HLA-A, B anc C antigen molecules blocked the lysis of EB virus-transformed target cells by EB virus-specific cytotoxic T cells reactivated in vitro. Blocking was mediated through binding of the antibodies to the target rather than to the effector cells and was maximal (75 to 85% inhibition of lysis) at saturating antibody concentrations. A similar blocking effect was also shown by a monoclonal antibody binding to beta 2-microglobulin, a molecule physically associated with HLA-A, B and C antigens on the target cell surface, but not by a monoclonal antibody binding to the non-HLA-associated leukocyte-common antigen. Saturating concentrations of monoclonal antibodies specific for common determinants on all HLA-DRw antigen molecules either had no effect at all upon EB virus-specific T cell cytotoxicity or caused a slight, but nonspecific, inhibition. The results demonstrate unequivocally that HLA-A, B and C antigens on the target cell surface are indeed the polymorphic elements which impose genetic restriction upon EB virus-specific cytotoxic T cell function.

Analysis of H-2 determinants recognized during the induction of H-Y-immune cytotoxic T cells by monoclonal antibodies in vitro

Monoclonal antibodies directed to the D region of H-2(k) when present during in vitro culture inhibit the generation of CBA/H and C3H.H-2(o) H-Y-immune cytotoxic T cells . Monoclonal antibodies directed to the I-A(k) and I-E(k) region specifically inhibited induction of CBA/H H-Y-immune cytotoxic T cells only when they were present simultaneously in culture. These findings show T helper cell requirement for CBA/H H-Y-immune cytotoxic T cell induction, and suggest that two I region-coded restriction antigens for T helper cells are involved.

The detection of influenza A virus antigens in cultured cells by enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was employed to investigate the expression of influenza A/Hong Kong/68 (H3N3) virus structural proteins on the surface of infected MDCK cells, and to detect viral antigens in culture media and cell extracts. Infected cells were fixed with 0.1 per cent glutaraldehyde before being examined for the presence of cell-surface antigens. Viral antigens were first observed on the surface of cells 4 hours after infection and reached a maximum 10-12 hours after infection, when measured by haemadsorption with chicken erythrocytes and by ELISA and immunofluorescence with hyperimmune antiserum to Hong Kong virus. A good correlation was found between the three assay systems. The presence of individual virion structural proteins on the cell surface was determined by ELISA using specific antibodies purified by differential affinity chromatography. Either or both or the internal matrix and nucleoprotein antigens were expressed from 2 to 6 hours after infection, with maximum expression after 2 hours, and the strain-specific and common antigenic determinants of haemagglutinin were observed on the cell surface from 4 hours after infection, and reached a maximum 8 to 10 hours after infection. Low levels of neuraminidase were detected between 4 and 8 hours after infection. Culture media and cell extracts were titrated by infectivity and haemagglutination assays, and by ELISA. Titres obtained from the culture media showed a close correlation between the three assay methods, with peak titres being attained 24 hours after infection. Viral antigens were first observed in cell extracts by ELISA 4 hours after infection, and infectious virions and haemagglutinin 2 hours later, but whereas maximum titres of infectious virus and haemagglutinin were found 10 hours after infection, the ELISA titre continued to rise until 24 hours after infection, which suggested that virus structural proteins were being accumulated in the cells after most of the progeny virions had been released. The results are discussed in terms of the potential use of ELISA in rapid virus diagnosis.

Cross-reactivity for different type A influenza viruses of a cloned T-killer cell line

Spleen cytotoxic T cells killing influenza virus-infected target cells are cross-reactive for the different type A influenza viruses, in contrast to the circulating antibodies, which show fine specificity for each A virus subtype variant. This finding has raised the question of whether a single T cell can recognize cells infected with all type A viruses. T-killer cell lines with specificity for alloantigens and the male Y antigen can be selected by means of growth factors present in the supernatant of T cells stimulated with concanavalin A (refs 3-7). We report here that we have been able to establish clones of mouse T cells killing target cells infected with influenza virus. Our cell line maintains the same specificity as the heterogeneous spleen cell population from infected mice, in as far as the T-killer cells are specific for A influenza virus, but do not discriminate between the different type A viruses. The cell line maintains H-2 restriction and does not kill cells infected with B influenza virus. The cells grow in the presence of T-cell growth factor and do not require antigen for growth although they maintain their receptors for type A virus. They can also be stimulated by irradiated T-helper cells from mice primed by type A influenza infection in the presence of type A virus-infected cells.

Cross-protection and cross-reactive cytotoxic T cells induced by influenza virus vaccines in mice

Subunit and intact influenza A virus vaccines have been compared with infectious virus in a mouse model for their ability to induce memory for cross-reactive cytotoxic T cell responses and to protect mice from challenge with different subtypes of influenza A virus. There is an overall correlation between secondary cytotoxic T cell responses and cross-protection. The most long-lasting and successful cross-protection was observed after intranasal infection with influenza virus A/X31 (H3 N2) that replicates efficiently in mice and induces high levels of memory for cross-reactive cytotoxic T cell responses. Short-lasting cross-protection and low levels of T cell-mediated cytotoxicity were associated with infection by A/USSR (H1 N1) virus, that replicates to lower titers in mice, or after multiple injections of inactivated whole virus vaccine. No cross-protection to challenge with heterologous influenza virus was detectable after 1-2 injections of HANA influenza subunit vaccine which failed to prime hosts for cytotoxic T cell responses. These findings may have important implications for vaccination strategy. If cytotoxic T cells play a role in the protection of humans from influenza, live attenuated vaccines should be considered instead of the currently recommended inactivated virus or subunit vaccines.