Experiments and speculation on antiviral specificity of T and B cells

Dual mechanisms of apoptosis induction by cytotoxic lymphocytes

Cytotoxic T lymphocytes and natural killer cells together comprise the means by which the immune system detects and rids higher organisms of virus-infected or transformed cells. Although differing considerably in the way they detect foreign or mutated antigens, these cells utilize highly analogous mechanisms for inducing target cell death. Both types of effector lymphocytes utilize two principal contact-dependent cytolytic mechanisms. The first of these, the granule exocytosis mechanism, depends on the synergy of a calcium-dependent pore-forming protein, perforin, and a battery of proteases (granzymes), and it results in penetration by effector molecules into the target cell cytoplasm and nucleus. The second, which requires binding of FasL (CD95L) on the effector cell with trimeric Fas (CD95) molecules on receptive target cells, is calcium independent and functions by generating a death signal at the inner leaflet of the target cell membrane. Exciting recent developments have indicated that both cytolytic mechanisms impinge on an endogenous signaling pathway that is strongly conserved in species as diverse as helminths and humans and dictates the death or survival of all cells.

Different roles for cytotoxic T cells in the control of infections with cytopathic versus noncytopathic viruses

The assessment of the role of T-cell-mediated cytotoxicity in immunity to viral infections has been difficult to address directly and therefore has been controversial. Recent experiments with perforin-deficient mice have shown that cytotoxicity is crucial for the resolution of infection with lymphocytic choriomeningitis virus but not for the resolution of infection with vaccinia, vesicular stomatitis, Semliki Forest or influenza virus. These findings may reflect the general pattern that T-cell-mediated cytotoxicity is crucial only for the resolution of infections with noncytopathic viruses, whereas infections with cytopathic viruses are mainly controlled by soluble mediators such as antibodies and interferons.

The roles of perforin- and Fas-dependent cytotoxicity in protection against cytopathic and noncytopathic viruses

In vitro, T cell-dependent cytotoxicity is mediated by two distinct mechanisms, one being perforin-, the other Fas-dependent. The contribution of both of these mechanisms to clearance of viral infections was investigated in mice for the non-cytopathic lymphocytic choriomeningitis virus (LCMV) and the cytopathic vaccinia, vesicular stomatitis (VSV) and Semliki forest (SFV) viruses. Clearance of an acute LCMV infection was mediated by the perforin-dependent mechanism without measurable involvement of the Fas-dependent pathway. For the resolution of vaccinia virus infection and for resistance against VSV and SFV, however, neither of the two pathways was required. These data suggest that perforin-dependent cytotoxicity mediated by T cells is crucial for protection against non-cytopathic viruses, whereas infections with cytopathic viruses are controlled by nonlytic T cell-dependent soluble mediators such as cytokines (IFN-gamma against vaccinia virus) and neutralizing antibodies (against VSV and SFV).

Pseudorabies virus-induced suppression of major histocompatibility complex class I antigen expression

The ability of pseudorabies virus (PrV) to down-modulate expression of major histocompatibility complex class I antigens in murine and porcine cells was investigated. When quantified by flow cytometry, surface expression of class I Kk and Dk antigens on PrV-infected cells decreased by 60% or more. Down-modulation was associated with a decrease in total cellular class I antigens, indicating regulation at the transcriptional or posttranscriptional level. PrV did not suppress expression of transferrin receptor, suggesting a selective regulatory mechanism.

Importance of cell-mediated immunity in Marek's disease and other viral tumor diseases

Cell-mediated immune (CMI) responses to viral tumor diseases are often used as examples of the importance of antiviral and antitumor immunity in chickens. Especially, reticuloendotheliosis virus (REV) and Marek's disease herpesvirus (MDV) are used as models to study the development of cytotoxic T-lymphocytes against viral and tumor antigens and activation of natural killer (NK) cells. Major histocompatibility complex Class I-restricted, antiviral cytotoxic T-lymphocytes expressing CD4-/CD8+ markers are induced after infection with REV. Thus far, this is the only example of Class I-restricted cytotoxic T-lymphocytes in chickens. Antiviral cytotoxic T-lymphocytes may be induced by infection with MDV or by vaccination, but conclusive evidence has not yet been provided. Antitumor responses have not been demonstrated against REV-induced tumors. Although Marek's disease is often used as an example for the importance of antitumor immunity, there is a lack of convincing data demonstrating antitumor immunity mediated by cytotoxic T-lymphocytes. Activation of NK cells by MDV infection or vaccination is probably an important part of CMI responses against Marek's disease viral antigens but not against tumor antigens.

Analysis of the kinetics of antiviral memory T help in vivo: characterization of short-lived cross-reactive T help

To evaluate the kinetics of functional effector and memory T help in vivo the effect of priming with one serotype of vesicular stomatitis virus-Indiana (VSV-IND) on the antibody response to a serologically distinct heterologous second serotype (VSV-New Jersey: VSV-NJ) was studied. Mice primed with VSV-IND 4 or 8 days before being given a second infection of VSV-NJ developed an earlier and enhanced IgG response to neutralizing determinants of the second VSV serotype. However, this enhanced response was not detected in mice primed 15 or more days prior to a second infection. After 15 days, mice challenged with the heterologous VSV-NJ mounted a strictly normal primary response without evidence of suppression. It was shown by in vivo time-kinetics experiments that efficient VSV cross-reactive T help, capable of enhancing the IgG response is short lived and cyclosporin A resistant. Adoptive transfer experiments demonstrated in the absence of experimental evidence for suppression that this short-lived capacity to enhance neutralizing IgG antibody responses is mediated by T cells. These findings have implications for understanding antiviral protection and immunological memory against related but serologically distinct viruses.

Assessment of the specificity of cytotoxic T lymphocytes for the nucleoprotein of Pichinde virus using recombinant vaccinia viruses

Pichinde virus (PV) infection of mice results in induction of a strong H-2 restricted, virus-specific cytotoxic T lymphocyte (CTL) response and rapid clearance of the virus. To define the specificities of CTL induced by PV infection, we constructed vaccinia virus recombinants containing cloned cDNAs corresponding to full-length (VVNP) and a truncated form (VVNP 51-561) of the nucleoprotein (NP) gene of PV. Radioimmunoprecipitation analysis of infected cell lysates indicated that VVNP expressed a PV-specific product identical in size to that of authentic NP, while vaccinia virus recombinants containing truncated NP produced a polypeptide consistent with the synthesis of amino acids 51-561 of Pichinde virus NP. Interestingly, cells infected with VVNP synthesized easily detectable, but much lower levels of nucleoprotein relative to both PV and VVNP51-561. Primary virus-specific CTL induced in three different strains of inbred mice following intravenous infection with PV were able to lyse syngeneic target cells infected with PV but did not markedly lyse syngeneic targets expressing full-length or truncated NP following recombinant vaccinia virus infection. Similarly, secondary anti-PV specific CTL generated following in vitro restimulation by PV or selectively restimulated with vaccinia recombinants did not significantly lyse target cells expressing NP. Further, infection of mice with VVNP and VVNP51-561 did not induce CTLs specific for PV and did not prime mice for the generation of memory anti-PV CTL in vivo. These results suggest that PV gene products other than NP, such as the GPC or L protein, contain the major target epitope(s) recognized by PV-specific CTL.

Virus-induced autoantibody response to a transgenic viral antigen

The induction of autoantibodies and their possible role in the pathogenesis of autoimmune disease are poorly understood. Involvement of infectious agents has been suspected, but direct evidence is sparse. Whether immunological unresponsiveness to self by antibody-forming B cells is maintained by clonal abortion, clonal anergy or suppression, or how the scenario of interactions between helper T cells, B cells and antigen-presenting cells is distorted in autoantibody responses, is being analysed and widely debated. To evaluate tolerance of neutralizing B-cell responses we used transgenic mice expressing the cell membrane associated glycoprotein (G) of vesicular stomatitis virus (VSV) as self-antigen. We show that autoantibodies to VSV-G cannot be induced by VSV-G in adjuvant or by recombinant vaccinia virus expressing VSV-G, but are triggered by infection with wild-type VSV. The data show that helper T-cell tolerance is crucial in maintenance of B-cell non-reactivity and that cognate T-B recognition is necessary to break tolerance of self-reactive B cells. These results may help to understand mechanisms of virus-induced autoimmunity.

H-2 restriction and serotype crossreactivity of anti-reovirus cytotoxic T lymphocytes (CTL)

Murine anti-reovirus cytotoxic T lymphocytes (CTLs) were analyzed for H-2 restricted recognition of virus infected target cells and for potential cross-reactivity with cells infected by reovirus serotype 1 (T1; Lang strain) or by serotype 3 (T3; Dearing strain). Anti-reovirus CTL specifically lysed virus infected cells and lysis was shown to be H-2 restricted by the H-2Dd, H-2Ld, H-2Kd, H-2Kb, and H-2Kk antigens. No H-2 antigens were identified which failed to restrict virus recognition by anti-reovirus CTL. Anti-T1 and anti-T3 CTLs were also shown to crossreact completely with cells infected with the opposite virus serotype. Thus, anti-reovirus CTLs are restricted by a broad spectrum of H-2 antigens and they detect common rather than unique structural components of these two viral serotypes.

Recognition of oligonucleotide-encoded T cell epitopes introduced into a gene unrelated to the original antigen

We have previously demonstrated that H-2Kd-restricted CTL specific for HLA-CW3 or HLA-A24 can recognize synthetic peptides corresponding to residues 170-182 of the HLA molecules. Synthetic oligonucleotides encoding region 170-182 of CW3 or A24 were inserted into the influenza nucleoprotein (NP) gene. We demonstrate herein that P815 (H-2d) cells transfected with the NP-oligo recombinant genes are specifically lysed by HLA-specific Kd-restricted CTL clones. Our results imply that there must be a high degree of flexibility for the expression of T cell epitopes in different molecular contexts.

Cellular immune response to hepatitis B virus antigens. An overview

It has been suggested that the cellular immune response to HBV antigens is responsible for hepatocellular injury in acute and chronic hepatitis B. However, definitive immunological studies have so far been hampered by the lack of appropriate model systems to study HBV antigen-specific T cells. The availability of highly purified and recombinant HBV antigens and of experimental techniques to maintain in continuous growth antigen-specific T cells derived not only from the peripheral blood but also from the liver should allow a better understanding of the fine immunopathogenetical mechanisms involved in viral clearance and liver damage. Whether some important biological characteristics of HBV antigens described in the mouse system, such as the high immunogenicity of the pre-S antigens and the capacity of the nucleocapsid of HBV to be a T cell-dependent and -independent antigen, are relevant to the immunopathogenesis of liver damage during natural HBV infection in man remains to be evaluated.

Synthetic peptides as antigens and competitors in recognition by H-2-restricted cytolytic T cells specific for HLA

The specificity of peptide recognition by a number of Kd-restricted CTL clones specific for HLA-CW3 or HLA-A24 was investigated. The CTL clones were derived from DBA/2 (H-2d) mice immunized with syngeneic P815 mouse cells transfected with genes encoding HLA-CW3 or HLA-A24 class I molecules. We had previously shown that CTL clones that lysed P815-CW3 transfectant target cells could lyse P815 (HLA-) target cells incubated with synthetic CW3 peptides corresponding to the COOH-terminal end of the alpha 2 domain. In the present study, we found that Kd-restricted CTL clones that lysed P815-A24 transfectant target cells recognized a synthetic peptide from the same region (residues 170-182) of the A24 molecule. CW3 and A24 differ by only one amino acid within this region. Recognition of CW3 or A24 peptides corresponded exactly with lysis of P815-HLA transfectants both for clones that mutually exclusively lysed CW3 or A24 transfectant target cells and for CW3/A24 crossreactive CTL clones. The latter CTL clones that lysed both CW3 and A24 transfectant target cells showed a clear preference for the peptide corresponding to the immunizing HLA allele. The homologous CW3 and A24 peptides could compete with each other for recognition, in contrast to a peptide from the same region of HLA-B7. Peptides from the corresponding region of the endogenous Kd and Dd/Ld molecules could also inhibit recognition of CW3 and A24 peptides. Competition with peptides apparently occurred at the level of the target cell. These results are consistent with a model whereby MHC class I molecules position protein fragments or peptides for specific recognition by T cells.

Cells expressing herpes simplex virus glycoprotein gC but not gB, gD, or gE are recognized by murine virus-specific cytotoxic T lymphocytes

To determine which viral molecule(s) is recognized by herpes simplex virus (HSV)-specific cytotoxic T lymphocytes (CTL), target cells were constructed which express individual HSV glycoproteins. A mouse L cell line, Z4/6, which constitutively expressed high levels of HSV type 2 (HSV-2) gD (gD-2) was isolated and characterized previously (D. C. Johnson and J. R. Smiley, J. Virol. 54:682-689, 1985). Despite the expression of gD on the surface of Z4/6 cells, these cells were not killed by anti-HSV-2 CTL generated following intravaginal infection of syngeneic mice. In contrast, parental Z4 or Z4/6 cells infected with HSV-2 were lysed. Furthermore, unlabeled Z4/6 cells were unable to block the lysis of HSV-2-infected labeled target cells. Cells which express HSV-1 gB (gB-1) were isolated by transfecting L cells with the recombinant plasmid pSV2gBneo, which contains the HSV-1 gB structural sequences and the neomycin resistance gene coupled to the simian virus 40 early promoter and selecting G418-resistant cell lines. One such cell line, Lta/gB15, expressed gB which was detected by immunoprecipitation and at the cell surface by immunofluorescence. Additionally, cells expressing HSV-1 gC (gC-1) or gE (gE-1) were isolated by transfecting Z4 cells, which are L cells expressing ICP4 and ICP47, with either the recombinant plasmid pGE15neo, which contains the gE structural sequences and the neomycin resistance gene, or pDC17, which contains the gC structural gene coupled to the gD-1 promoter. A number of G418-resistant cell lines were isolated which expressed gC-1 or gE-1 at the cell surface. Anti-HSV-1 CTL generated following footpad infection of syngeneic mice were unable to lyse target cells expressing gB-1 or gE-1. In contrast, target cells expressing very low levels of gC-1 were killed as well as HSV-1-infected target cells. Furthermore, infection of gC-1-transformed target cells with wild-type HSV-1 or a strain of HSV-1 that does not express gC did not result in a marked increase in susceptibility to lysis. These results suggest that murine class I major histocompatibility complex-restricted anti-HSV CTL recognize gC-1 but do not recognize gB, gD, or gE as these molecules are expressed in transfected syngeneic target cells. The results are discussed in terms of recent evidence concerning the specificity of antiviral CTL.

Antibodies against the two serotypes of vesicular stomatitis virus measured by enzyme-linked immunosorbent assay: immunodominance of serotype-specific determinants and induction of asymmetrically cross-reactive antibodies

The serological relationship between the two vesicular stomatitis virus (VSV) strains Indiana (VSV-Ind) and New Jersey (VSV-NJ) were analyzed by using an enzyme-linked immunosorbent assay (ELISA). Immunoglobulin G responses, defined by their resistance to treatment with 2-mercaptoethanol, were assessed by ELISA by using sucrose gradient-purified VSV or purified VSV glycoproteins (G) as antigens. When low doses (10(6) PFU) of live VSV or 10(8) PFU of UV-inactivated virus were given intraperitoneally (i.p.), only non-cross-reactive antibody responses were observed in a primary immune response. However, when 10(6) PFU of live VSV were injected intravenously (i.v.), cross-reactive antibodies were generated; anti-VSV-NJ antibodies cross-reacted more against VSV-Ind than did anti-VSV-Ind antibodies against VSV-NJ. When 10(8) PFU of live VSV or UV-inactivated VSV mixed with complete Freund adjuvant was given i.p., high levels of cross-reactive antibodies detectable by ELISA were induced in primary and secondary responses. When purified G protein was used instead of purified whole virus in the ELISA, the cross-reactivity was found to be asymmetrical after immunization with live VSV given i.v. but not after i.p. inoculation; anti-VSV-NJ sera bound almost equally well to VSV-Ind G protein, whereas anti-VSV-Ind sera bound virtually exclusively to the G protein of the homologous serotype. The data suggest that immunization with VSV given i.p. results in a more specific, i.e., less cross-reactive, response than that either after i.v. infection or after the virus antigen is made available in great amounts or if it persists for prolonged periods when given i.p. together with complete Freund adjuvant. The unique determinants were immunodominant because they induced antibodies preferentially, whereas partially shared determinants induced antibody responses asymmetrically, more slowly, and with lower titers. Interestingly, the asymmetric cross-reactivity of anti-VSV antibodies, as measured by ELISA, against purified VSV G was opposite that observed for cytotoxic T cells.

Searching for MHC-restricted anti-viral antibodies: antibodies recognizing the nucleoprotein of influenza virus dominate the serological response of C57BL/6 mice to syngeneic influenza-infected cells

An attempt has been made to generate monoclonal antibodies which recognize the same target structures on influenza-infected cells as those seen by cytotoxic T lymphocyte (CTL) receptors. Such antibodies, if they mimicked the T cell receptor specificity, would be expected to be both virus specific and restricted in their binding by the major histocompatibility complex (MHC) antigens. Approximately 200 hybridomas from C57BL/6 (H-2b) mice primed and boosted with influenza virus (X-31)-infected EL4 (a C57BL/6 T cell lymphoma) were screened for reactivity on infected and uninfected cells of different MHC haplotypes. Of the 10 hybridoma antibodies which were identified as being reactive with X-31-infected EL4, but not uninfected EL4, all reacted equally well with X-31-infected cells of H-2b, H-2d and H-2k haplotypes, indicating a lack of MHC restriction in their recognition of the infected cells. Unexpectedly, 7 of the 10 monoclonal antibodies were found to react specifically with the purified influenza virus nucleoprotein (NP), a predominant viral antigen in CTL recognition of infected cells. Fluorescence-activated flow cytometry confirmed that these antibodies were able to recognize NP serological determinants on the surface of viable, infected cells, but the anti-NP antibodies were unable to block the lytic activity of an NP-specific CTL clone.

T cell cross-reactivity among viruses of the paramyxoviridae

Blastogenesis and delayed-type hypersensitivity assays were used to examine mouse T cell responses to five viruses representing the three genera of the Paramyxoviridae. Cross-reactive T cell responses were observed in a lympho-proliferative assay for measles, mumps, respiratory syncytial, canine distemper and parainfluenza type 3 virus. Confirmation of T cell cross-reactivity among measles, mumps and respiratory syncytial virus was obtained with a delayed-type hypersensitivity test. These results show that T cell cross-reactivity is common for Paramyxoviridae viruses, even though these viruses show virtually no inter-genus antibody cross-reactivity. The cross-reactivity among respiratory syncytial, measles and mumps virus at the T cell level may have implications for usage of the attenuated measles/mumps/rubella (MMR) vaccine. Respiratory syncytial virus is contacted by many children before they receive the MMR vaccine and T cells induced by respiratory syncytial virus may influence subsequent development of immunity to measles and/or mumps virus.

N protein is the predominant antigen recognized by vesicular stomatitis virus-specific cytotoxic T cells

The specificity of anti-vesicular stomatitis virus (VSV)-specific cytotoxic T cells was explored with cell lines expressing VSV genes introduced by electroporation. Low levels of nucleocapsid (N) protein were detected on the surface of VSV-infected cells, but N protein could not be detected on the plasma membrane of transfected EL4 cells. Intracellular N protein was detectable by enzyme-linked immunosorbent assay or immunoprecipitation in some of the transfected cell lines but not in others, unless the transfected genes were induced by sodium butyrate. However, all of the stably transfected EL4 cell lines expressing the VSV-Indiana N protein were efficiently lysed by serotype-specific and cross-reactive anti-VSV cytotoxic T cells (CTLs). Primary cross-reactive anti-VSV CTLs appeared to be specific solely for N protein, based on cold-target competition assays using infected and transfected target cells. Cell lines expressing 100- to 1,000-fold less N protein than did VSV-infected cells were efficiently lysed by both primary and secondary anti-VSV CTLs. Cell lines expressing 100-fold less G protein than did VSV-infected cells were not lysed by either population of effectors. Significantly, cold-target competition studies with secondary CTLs demonstrated that N protein-expressing cell lines were more efficient competitors than were VSV-infected cells even though the latter expressed 100- to 1,000-fold more N protein. This was not an artifact of viral infection since infection of the transfected cell lines did not affect their ability to compete. The possibility that cell lines constitutively expressing internal virus proteins present antigen more effectively than infected cells do is discussed.

The preparation and characterization of anti-peptide heteroantisera recognizing subregions of the intracytoplasmic domain of class I H-2 antigens

Peptides corresponding to each of the three intracytoplasmic exons (i.e. exons 6, 7 and 8) of the murine class I H-2Kb gene were synthesized, coupled to bovine serum albumin and used as immunogens in rabbits. In each case the antisera were found to react with the immunizing peptide coupled to a heterologous carrier, and recognized class I heavy chains electrophoretically transferred from SDS-polyacrylamide gels to nitrocellulose. Immunoprecipitation of class I antigens from Nonidet P-40 (NP-40) solubilized EL-4 (H-2b) tumour cells by each of the antisera reflected their ability to recognize the corresponding determinants in non-denatured class I molecules. The same sera were also able to immunoprecipitate class I molecules from NP-40 solubilized RDM-4 (H-2k) and P815 (H-2d) tumour cells, indicating the cross-reactive nature of these antisera for different class I alleles. In addition to reacting with the class I heavy chain in its conventional form as a dimer with beta 2-microglobulin, the antiserum specific for the exon 8 peptide was able to react with "free" (i.e. non-beta 2-microglobulin-associated) class I heavy chains. Thus, a unique set of immunological reagents has been prepared which offer a new approach to studying the structural and functional features of the cytoplasmic domain of class I H-2 antigens.

Primary antibody responses to a well-defined and unique hapten are not enhanced by preimmunization with carrier: analysis in a viral model

We used a viral model to reexamine classical experiments showing that mice previously primed with a "carrier" molecule alone and then challenged with the carrier-hapten conjugate exhibited an enhanced antihapten antibody response. Mice were primed with live or UV-inactivated vesicular stomatitis virus (VSV) Indiana (Ind) serotype with or without complete Freund's adjuvant. After challenge with VSV New Jersey (NJ), these mice developed a secondary-type IgG response, measured by antibody binding in an ELISA, against both VSV-Ind and VSV-NJ. The same result was found for the reciprocal experiments where mice were primed with VSV-NJ. Similarly, when mice were primed with live VSV, UV-inactivated VSV, or purified VSV glycoprotein G of Ind or NJ serotype and later were challenged with dinitrophenyl (N2ph)-conjugated, UV-inactivated VSV or with N2ph-conjugated G protein of either serotype, they exhibited a secondary-type anti-N2ph antibody response as demonstrated by the binding of IgG to dinitrophenylated bovine serum albumin measured by ELISA. In contrast, when neutralizing antibody responses were monitored, VSV-Ind-primed mice challenged with VSV-NJ developed a strictly primary type of anti-VSV-NJ response and vice versa. We conclude that preexistent helper T cells specific for shared carrier determinants do not improve virgin B-cell responses specific for "new," unique determinants that are the target for the biologically relevant neutralizing antibodies. These findings suggest that priming of B cells rather than of helper T cells may be of importance to induce protective immunity mediated by antibodies.

Cytotoxic T cells recognize fragments of the influenza nucleoprotein

Recent work has shown that a major population of murine influenza A specific cytotoxic T lymphocytes (CTL) recognize the viral nucleoprotein. In order to investigate the mechanism by which this nonglycoprotein component of the virus is recognized by CTL, a series of deletion mutants of an A virus NP gene were studied. The results showed that CTL recognize three distinct epitopes of the NP molecule. Both N- and C-terminal fragments of the protein are transported, independently of each other, to the site of recognition by CTL. These findings imply that a mechanism may exist for transport to the cell surface and presentation to CTL, of viral proteins and protein fragments that lack defined signal sequences.

Genetic complexity and expression of human class II histocompatibility antigens

The genes encoding nearly all of the serologically defined class II antigens of the major histocompatibility complex have been isolated. Three class II loci have been studied in great detail. The DR region contains a single alpha gene and 3 beta chain genes, 1 of which is a pseudogene. The DR alpha chain gene has been linked to a DR beta gene which encodes a beta protein which contains the serological determinant MT3. A second cosmid cluster contains 2 beta genes, 1 of which encodes the DR4 allospecificity. The identification of these genes has been made by the comparison of amino terminal sequences of DR molecules obtained from a DR4 cell line and the deduced protein sequences of the beta 1 exons from cosmid and phage clones. A conserved element including the promoter and signal sequence is found at the 5' end of each of the 3 DR beta genes. Additionally, this element occurs three more times in the DR region, raising the question of whether additional beta chain genes might be found. The DQ region contains 2 pairs of genes, 1 of which encodes the DQ antigen. The 2nd pair of genes, called DX alpha and beta, appears to be capable of expressing a DQ-related product, although, to date, there is no evidence for its expression. The DP region also contains 2 pairs of genes. One pair encodes the DP antigen while the 2nd alpha-beta pair is shown to be composed of pseudogenes. The location of polymorphic regions in these genes and aspects of their relationship to the serology, evolution, and function of the class II MHC are discussed. The control of expression of class II genes by gamma-interferon has been examined. The promoters of class II genes are characterized by two conserved sequences common to all alpha and beta chain genes as well as by conserved sequences specific for either alpha or beta chain genes. In addition to studies of expression by DNA-mediated gene transformation, a system for the gene transfer of MHC antigens utilizing transmissible retrovirus vectors is described. Retrovirus vectors have been used to transmit DR alpha, DR beta, and the invariant chain (gamma) sequences to recipient cells with resultant expression of these proteins.

Preferential lymphocyte-mediated cytotoxicity of syngeneic target cells in chickens bearing tumors induced by avian sarcoma virus

Splenic lymphocytes from chickens bearing tumors induced by avian sarcoma virus are able to cause the specific killing of cultured avian sarcoma cells. This cytotoxicity appears to follow classical patterns of syngeneic restriction. Little or no specific killing of tumor targets occurred when spleen cells from one inbred line of chickens were tested against allogeneic targets, although syngeneic killing proceeded relatively efficiently. Other patterns of immune reactivity did not appear to be syngeneically restricted. Namely, sera from tumor-bearing hosts were equally reactive in indirect immunofluorescence assays with syngeneic and allogeneic target cells. And, peripheral blood lymphocytes from sensitized hosts could be stimulated equally well by tumor cell culture fluids of allogeneic or syngeneic origin.

Inhibition of hapten-specific cytotoxic T cell recognition by monoclonal anti-hapten antibodies

The T cell-mediated cytotoxic response against autologous cells modified with the sulfhydryl reagent I-AED (N-iodoacetyl-N'-(5-sulfonic-1-naphthyl) ethylene diamine) is hapten specific and H-2 restricted (Levy, R. B., Shearer, G. M., Richardson, J. C. and Henkart, P. A., J. Immunol. 1981. 127: 523). We have produced a monoclonal antibody (V-6-3, IgM) which binds to AED-modified cells and proteins. Competition experiments by free hapten indicated that the binding was AED specific. The effect of the mAb on AED-specific cytotoxic T cell recognition at the effector and induction stage has been examined. Anti-AED mAb inhibited the cell-mediated lysis of some but not all AED-specific, H-2b-restricted long-term cytotoxic T cell clones and of bulk-cultured C57BL/6 anti-AED-self effector cells. This blocking was not due to nonspecific agglutination of targets since lysis of AED-modified target cells by alloreactive effector cells was not affected by this mAb under comparable conditions. Furthermore anti-AED mAb specifically inhibited the antigen-induced proliferation of AED-specific long-term cytotoxic T cell clones and the generation of AED-specific cytotoxic effector cells in secondary cultures. This monoclonal anti-AED antibody bound to cells modified by the recently described aminoreactive reagent AED-NH2 (Takai, Y., Mizuochi, H., Fujiwava, H. and Hamaoka, T., J. Immunol. 1984. 132: 57); these same target cells were, however, not lysed by AED-SH-specific cytotoxic T cell clones.

Cell-mediated damage to helminths

Although it is difficult to draw any sweeping conclusions that would be applicable to all helminth infections, the main features that are emphasized in this review may be summarized briefly. Pathogenic helminths, although extremely diverse in structure and behaviour, have one common feature, namely that they present to the host's defenses large, non-phagocytosable surfaces. Because of this, they are susceptible to a range of effector mechanisms differing either quantitatively or qualitatively from those that are active against other parasites or against normal or abnormal host cells. As an extreme example, the various types of cytotoxic lymphocyte, with one interesting exception, are inactive against helminths. Instead, helminth infections are characterized by high IgE responses and increased numbers of circulating eosinophils. Such eosinophils are activated, and show a marked capacity to kill a variety of target helminths in vitro. Further activation may occur in response to mast cell mediators released as a result of IgE-dependent degranulation; and IgE, as well as IgG and complement, can mediate eosinophil attachment and killing. It may therefore be suggested that the eosinophil/IgE/mast cell axis represents a powerful host defense against helminth infections. IgE can also mediate macrophage-dependent killing of several helminths, a process which involves a functional change in the macrophage, resembling activation. Although eosinophil-mediated and IgE-dependent macrophage-mediated effects are particularly potent, other effector cells are not excluded: in certain circumstances, neutrophils and conventionally activated macrophages may be equally or more effective. Neutrophils appear to act solely by oxidative killing mechanisms, whereas degranulation and the release of toxic granule contents is equally or more important in eosinophil-mediated damage. Different stages of different helminths vary in their degree of susceptibility to different mechanisms. Eosinophils appear to be somewhat less active than neutrophils against ensheathed nematodes, whereas trematodes and exsheathed nematodes are highly susceptible to eosinophil attack. In many experimental helminth infections, studies in vivo suggest a role for antibody-dependent cell-mediated immune effector mechanisms. The identity of the effector cell is difficult to establish because of a lack of techniques for specific manipulation of individual cell types, but histological studies frequently point to a strong eosinophil or macrophage involvement. The development and analysis of in vitro assays allows the study of immune effector mechanisms in man.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytotoxic T cell recognition of the influenza nucleoprotein and hemagglutinin expressed in transfected mouse L cells

L cells expressing either the A/NT/60/68 nucleoprotein or the A/PR/8/34 (H1) hemagglutinin by DNA mediated gene transfer were used to investigate recognition by influenza A specific cytotoxic T lymphocytes (CTL). A subpopulation of CTL that recognized the H1 hemagglutinin was detected in mice primed with either A/PR/8/34 (H1N1) or A/JAP/305/57 (H2N2) influenza viruses. However, neither CTL from mice primed with A/NT/60/68 (H3N2) nor the recombinant virus X31 (H3N2) showed any activity on L cells expressing H1. These results showed that the majority of fully crossreactive CTL do not recognize the hemagglutinin molecule. A comparison between nucleoprotein and hemagglutinin transfected L cells reveals the nucleoprotein as the major target for CTL that are crossreactive on the three pandemic strains of human influenza A virus.

Induction of delayed-type hypersensitivity to measles virus in mice

Intracutaneous injection of inactivated measles virus (MV) into hind footpads of BALB/c mice infected 5 to 11 days previously with MV produces a strong delayed-type hypersensitivity (DTH) response. Pretreatment of mice with cyclophosphamide (CP) results in a significantly stronger response. In CP-pretreated mice, the optimal infecting dose of live MV and the restimulating amount of inactivated MV are approximately 10(7) plaque-forming units and 2 micrograms/mouse, respectively. The optimal time after infection for measuring DTH to MV is 7 days, while the optimal CP-pretreatment concentration is 200 mg/kg. The DTH response generated by MV is specific and not caused by fetal calf serum or Vero cell antigens. MV DTH is transferable to uninfected mice with lymph node cells. Transfer of DTH is sensitive to treatment with anti-Thy 1.2 serum plus complement, indicating the response is T cell dependent. With this sensitive assay for measuring cell-mediated immunity to MV, it will now be possible to analyze T cell cross-reactivity among paramyxoviruses and assess viral cell-mediated immunity in mice infected with neuroadapted MV.

Frequency analysis of cytolytic T lymphocyte precursors (CTL-P) generated in vivo during lethal rabies infection of mice. II. Rabies virus genus specificity of CTL-P

Cytolytic T lymphocyte precursors (CTL-P) were sensitized in vivo by intraplantar infection of C57BL/6 mice with a lethal dose of rabies virus, strain ERA (ERA). As a result of sensitization CTL-P matured to interleukin-receptive CTL-P (IL-CTL-P) that could be expanded in vitro to Thy-1+, Lyt-2+ CTL clones in the presence of IL without subjection to antigen-driven selection. After infection with ERA, IL-CTL-P-derived CTL lysed fibroblasts infected with rabies virus but not those infected with another rhabdovirus, the vesicular stomatitis virus. These CTL, however, did not discriminate between fibroblasts infected with the serologically closely related laboratory strains of classic rabies virus, ERA and HEP-Flury, and the serologically distinct rabies-related African isolate Mokola. This finding implies that in vivo sensitized IL-CTL-P recognize common genus-specific determinants expressed on cells infected with members of the lyssavirus genus.

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.

Virus specificity of cytotoxic T lymphocytes generated during acute lymphocytic choriomeningitis virus infection: role of the H-2 region in determining cross-reactivity for different lymphocytic choriomeningitis virus strains

We have compared the relatedness of five different strains of lymphocytic choriomeningitis virus (LCMV) as assessed by LCMV-specific cytotoxic T lymphocytes (CTL). Several different mouse strains were injected with each of the five LCMV strains, and the cross-reactivity of virus-specific CTL generated during the acute infection was tested by killing on a panel of target cells infected with the various LCMV strains. We found that the cross-reactivity pattern of LCMV-specific CTL generated in mice of H-2d haplotype (BALB/c WEHI and DBA/2) was strikingly different from that in mice of H-2b haplotype (C57BL/6 and C3H.Sw/Sn), suggesting that the fine specificity of LCMV-specific CTL is a function of the H-2 region. The characteristic cross-reactivity patterns were also observed in (C57BL/6 X DBA/2)F1 mice, demonstrating that the repertoire of the H-2b- and H-2d-restricted LCMV-specific CTL is not changed as a result of complementation by gene products of the other major histocompatibility haplotype. Studies with congenic BALB.B10 and (BALB.B10 X BALB/c)F1 mice firmly established that the characteristic cross-reactivity patterns of LCMV-specific CTL map to the H-2 region and are not influenced by background genes outside the major histocompatibility locus. These results suggest that LCMV determinants seen in the context of H-2d-restricting elements are different from those seen in the context of H-2b-restricting elements. Moreover, our studies show that CTL can be used as probes for dissecting differences among various LCMV strains, but the degree of relatedness between the different LCMV strains is not absolute when measured by CTL recognition. Since the H-2 region regulates the fine specificity of CTL generated during LCMV infection in its natural host, the degree of cross-protective immunity developed during a viral infection apparently depends on the major histocompatibility haplotype. The importance of these findings lies in understanding susceptibility or resistance of various host populations to viral infections and in designing vaccination programs to provide immunity.

Influence of multiple genes on the magnitude of the antibody response to bacterial polysaccharide antigens

Studies conducted with F1 and F2 progeny of crosses between strains of inbred mice that differ greatly in their capacity to make an antibody response to type III pneumococcal polysaccharide, dextran B-1355, and lipopolysaccharide from Escherichia coli 0113 have shown that multiple genes influence the magnitude of the antibody response to these antigens. Other studies with hybrids derived from crosses between C3H/HeJ, CBA/N, and RIIIS/J mice have indicated that the genetic defects characteristic of these strains of mice are dissimilar and unlinked and that autosomal, as well as X-linked, genes control serum immunoglobulin M in unimmunized mice.

Some recent advances in biology and diseases manifested by abnormal immune regulation

Diseases manifested by abnormal immune regulation represent perturbations of a system of heterologous genetic recombination. This heterologous recombination is mediated by plasmids and viruses, facilitated by immune multigene families, and may be affected by physical factors. Heterologous recombination facilitates individual adaptation to new environmental challenges, thereby promoting survival and evolution. Present evidence which supports this hypothesis and a means to test it are outlined. The medical implications of the hypothesis are briefly discussed.

HLA and disease

This review describes the greater portion of a large number of new studies on HLA and disease association which has appeared in the literature since 1979. The majority of these are concerned with the association of certain diseases with class II major histocompatibility complex antigens. The possible biologic significance of these associations in terms of their probable etiology appears to be the prevailing theme. Current thinking regarding certain heritable diseases is described. It seems that although much has been done to resolve the genetics of insulin-dependent diabetes mellitus, other diseases such a multiple sclerosis still remain a mystery. Doubtlessly, much will be gained from DNA cloning and sequencing studies proposed for the future. A great deal of new information has been obtained relative to HLA itself. New loci have been postulated in the HLA-D/DR region through the use of powerful immunochemical procedures made possibly by the advent of modern technological advances. The impact of these developments on our understanding of the function of the MHC in man and its possible relationship to disease are discussed.

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.

The cytolytic T lymphocyte response to the murine cytomegalovirus. II. Detection of virus replication stage-specific antigens by separate populations of in vivo active cytolytic T lymphocyte precursors

During the acute cytolytic T lymphocyte (CTL) response of mice to infection with the murine cytomegalovirus two independent populations of activated interleukin-receptive CTL precursors can be demonstrated. One population is specific for cell membrane-incorporated viral structural antigens, whereas the second population detects an antigen, whose appearance is correlated with the synthesis of viral immediate early proteins. Since this new type of antigen is only defined by lymphocyte recognition, it is referred to as the lymphocyte-detected immediate early antigen (LYDIEA). Expression of immediate early antigen precedes the production of viral progeny and, therefore, it is possible that LYDIEA-specific CTL could serve as indicator cells for the very first activities of the viral genome, even during nonproductive infection.

Direct demonstration that cytotoxic T lymphocytes recognize conformational determinants and not primary amino acid sequences

The bm 1 H-2Kb mutant differs from the parental strain C57BL/6 (B6) only at amino acid (AA) positions 152, 155, and 156 of the H-2K molecule. The H-2Ld molecule is structurally identical with the H-2 Kbm1 molecule from positions 146-162, thus including all three AA substitutions in Kbm1. In direct lysis and monolayer adsorption studies, B6 anti-bml cytotoxic T lymphocytes (CTL) were shown to include at least five distinct CTL subsets of the following specificities. (a) Uniquely reactive with Kbm1; (b) cross-reactive with Kk; (c) cross-reactive with Dk; (d) cross-reactive with H-2d minus Ld, and (e) cross-reactive with Ld. If B6 anti-bm1 CTL were directed against the primary AA-sequence difference, then all five subsets are expected to react with Ld. However, four out of five CTL subsets including a major population uniquely directed against Kbm1 failed to react with Ld. These findings strongly strengthen the notion that CTL recognize conformational determinants and not primary AA sequences.

Lack of shared lymphocyte-stimulating determinants between H-2I and HLA-D/DR using mouse primed lymphocyte typing cells

A number of anti-H-2 alloantisera containing antibody reactive with I region gene products (Ia) of the major histocompatibility complex cross-react with determinants expressed by human peripheral blood B lymphocytes. Such data have led to the conclusion that Ia and DR antigens share cross-reacting determinants. We have attempted to generate mouse primed T lymphocyte populations specific for defined I region gene product determinants which concomitantly recognize DR determinants on human peripheral blood leukocytes in primed lymphocyte typing (PLT) analysis. Mouse PLT cells were generated in primary MLC using strain combinations identical to those in which positive mouse/human cross-reacting antisera have been obtained. The resulting PLT cells exhibited strong, yet specific, secondary MLC responses against mouse cells expressing the Ia determinants used as the primary stimulus. In contrast, when examined on panels of human peripheral blood leukocytes, no reactivity was detected. This lack of cross-reactivity suggests that mouse T cells primed toward Ia determinants do not regularly recognize cross-reacting determinants of DR or D-associated antigens expressed on human PBLs. Consequently, mPLT cells are not a useful reagent in defining HLA-D region polymorphism.

Temperature-sensitive mutant of coxsackievirus B3 establishes resistance in neonatal mice that protects them during adolescence against coxsackievirus B3-induced myocarditis

Inoculation of neonatal CD-1 mice by multiple routes with an amyocarditic temperature-sensitive (ts) mutant (ts 1) derived from a myocarditic parent variant of coxsackievirus B3 (CVB3(m)) resulted in approximately half of the neonates surviving to adolescence. Challenge of the ts 1 survivors with CVB3(m) did not induce myocarditis, as assessed by histological examination of heart tissues. Virus was not detected in heart tissues of adolescent ts 1 survivors, but inoculation of these mice with CVB3(m) resulted in virus concentrations similar in titers to those found in CVB3(m)-inoculated normal adolescent mice. The ts 1 survivors did not contain detectable levels of anti-CVB3(m) neutralizing antibody, but upon challenge with CVB3(m) they produced antibody more rapidly and to higher titers than did normal CD-1 adolescents after primary inoculation with CVB3(m). Cell-mediated immunity in ts 1 survivors was compared with that of normal mice after challenge with CVB3(m). The capacity for production of migration inhibitory factor was assessed by the agarose droplet cell migration inhibition assay, using peritoneal exudate cells and a CVB3(m) cell lysate or KCl-extracted antigens from heart tissues of CVB3(m)-inoculated mice. Migration inhibitory factor activity was not detected in cultures of splenic leukocytes from ts 1 survivors of CVB3(m)-inoculated ts 1 survivors, but it was readily detected in cultures of splenic leukocytes from CVB3(m)-inoculated normal adolescent mice. The [(3)H]thymidine stimulation assay, performed with splenic lymphoid cells and purified CVB3(m) particles, revealed that lymphocytes from normal mice, whether inoculated with CVB3(m) or not, were not stimulated by CVB3(m) particle antigens, whereas lymphoid cells from a significantly higher proportion of ts 1 survivors, whether inoculated with CVB3(m) or not, responded with a stimulation index >/=2.0. The cells responding with positive stimulation were T lymphocytes. A higher proportion of normal mice and ts 1 survivors, both inoculated with CVB3(m), contained splenic cytotoxic T lymphocytes with higher reactivity against CVB3(m)-infected neonatal skin fibroblasts than against normal skin fibroblasts, as assessed by a (51)Cr release assay. The group of uninoculated ts 1 survivors present as a high proportion of individuals with cytotoxic T-lymphocyte reactivity against both uninoculated and CVB3(m)-inoculated skin fibroblasts. However, ts 1 survivors and normal mice possessed the same proportions of splenic lymphocytes carrying either allele for Lyt 1 and Lyt 2 surface markers. The results suggest two mechanisms by which ts 1 survivors exhibit resistance to CVB3(m) induction of myocarditis, namely, the rapid production of high-titered anti-CVB3(m) neutralizing antibody in response to CVB3(m) inoculation and altered cell-mediated immune responses against CVB3(m)-induced viral or novel cellular antigens. The data are compatible with the notion that an immune deviation mechanism, thought to be controlled through a mechanism requiring suppressor cell activity which inhibits macrophage activation in ts 1 survivors, protects these mice from induction of myocarditis.

Lymphocytotoxicity against autologous hepatocytes and membrane-bound IgG in viral and autoimmune chronic active hepatitis

Membrane-bound IgG and lymphocytotoxic activity of total, T-enriched and T-depleted lymphocytes, using autologous hepatocytes have been evaluated in: (a) 31 patients with chronic active hepatitis (CAH) (six autoimmune and 25 hepatitis B virus - HBV-related); (b) five patients with inactive alcoholic cirrhosis; and (c) nine subjects with normal hepatic histology. Lymphocytotoxicity was positive in 83% of autoimmune CAH and 68% of HBV-related cases; it was confined to the T-depleted subpopulation in the first group, while it was present in both the T-enriched and T-depleted subpopulations in 81% of HBV-related cases. Membrane-bound IgG was present in 58% of group (a) and in none of the other groups. A linear pattern was found in four out of five autoimmune CAH patients with positive lymphocytotoxic activity. The autoimmune patient with lymphocytotoxic activity within the normal range did not show any membrane fluorescence. Among HBV-related CAH patients, 13 presented a granular pattern, two an associated granular and linear pattern and ten were negative. These data suggest that different lymphocytotoxic mechanisms are involved in the two forms of CAH studied.

Cell-surface antigenic modifications with trinitrophenyl sulfonate versus trifluoromethyl-dinitrophenyl sulfonate

The aim of the work was to justify the use of trifluoromethyl-dinitrobenzene sulfonate (CF3-DNBS) modification rather than trinitrobenzene-sulfonate (TNBS) modification, so as to be able to take advantage of the presence of fluorine atoms in the analogue, which allow the analysis of the hapten-carrier bonds by 19F-NMR nuclear magnetic resonance. Cell-surface antigenic modifications brought about by exposure to TNBS or CF3-DNBS were found to be immunologically cross-reactive, both in cell-mediated lymphocytotoxicity and in indirect immunofluorescence. The extent of haptenic derivatizations was found to be of the same order of magnitude, as appraised both by quantitative-absorption studies or by using radioactive hapten, provided that the less chemically reactive CF3-DNBS was used at the concentration of 10 mM and TNBS at the concentration of 1 mM. However, only TNBS-modified cells were sensitive to destruction by antibody-plus-complement-mediated cytotoxicity.