Murine cytotoxic T-cell response to alphavirus is associated mainly withH- 2D ( k )

Alphaviruses: Host pathogenesis, immune response, and vaccine & treatment updates

Human pathogens belonging to the Alphavirus genus, in the Togaviridae family, are transmitted primarily by mosquitoes. The signs and symptoms associated with these viruses include fever and polyarthralgia, defined as joint pain and inflammation, as well as encephalitis. In the last decade, our understanding of the interactions between members of the alphavirus genus and the human host has increased due to the re-appearance of the chikungunya virus (CHIKV) in Asia and Europe, as well as its emergence in the Americas. Alphaviruses affect host immunity through cytokines and the interferon response. Understanding alphavirus interactions with both the innate immune system as well as the various cells in the adaptive immune systems is critical to developing effective therapeutics. In this review, we summarize the latest research on alphavirus-host cell interactions, underlying infection mechanisms, and possible treatments.

Gamma-Irradiated Influenza A Virus Provides Adjuvant Activity to a Co-Administered Poorly Immunogenic SFV Vaccine in Mice

Many currently available inactivated vaccines require “adjuvants” to maximize the protective immune responses generated against the antigens of interest. Recent studies in mice with gamma-irradiated influenza A virus (γ-FLU) have shown its superior efficacy compared to other forms of inactivated FLU vaccines and its ability to induce both potent interferon type-I (IFN-I) responses and the IFN-I-associated partial lymphocyte activation. Commonly, IFN-I responses induced by adjuvants, combined in vaccine preparations, have been shown to effectively enhance the immunogenicity of the antigens of interest. Therefore, we investigated the potential adjuvant activity of γ-FLU and the possible effect on antibody responses against co-administrated antigens, using gamma-irradiated Semliki Forest virus (γ-SFV) as the experimental vaccine in mice. Our data show that co-vaccination with γ-FLU and γ-SFV resulted in enhanced SFV-specific antibody responses in terms of increased titers by sixfold and greater neutralization efficacy, when compared to vaccination with γ-SFV alone. This study provides promising evidence related to the possible use of γ-FLU as an adjuvant to poorly immunogenic vaccines without compromising the vaccine efficacy of γ-FLU.

In vivo elimination of MHC-I-deficient lymphocytes by activated natural killer cells is independent of granzymes A and B

NK cells kill target cells mainly via exocytosis of granules containing perforin (perf) and granzymes (gzm). In vitro, gzm delivery into the target cell cytosol results in apoptosis, and induction of apoptosis is severely impaired in the absence of gzm A and B. However, their importance for in vivo cytotoxicity by cytotoxic T cells has been questioned. We used an in vivo NK cytotoxicity assay, in which splenocytes from wild-type and β(2)microglobulin-deficient (MHC-I(neg)) mice are co-injected into recipients whose NK cells were activated by virus infection or synthetic Toll-like receptor ligands. Elimination of adoptively transferred MHC-I(neg) splenocytes was unimpaired in the absence of gzmA and gzmB, but dependent on perforin. This target cell rejection was NK cell dependent, since NK cell depletion abrogated it. Furthermore, target cell elimination in vivo was equally rapid in both wild-type and gzmAxB-deficient recipients, with the majority of specific target cells lost from lymphoid tissue within less than one to two hours after transfer. Thus, similar to T cell cytotoxicity, the contribution of gzmA and B to in vivo target cell elimination remains unresolved.

Restricted Semliki Forest virus replication in perforin and Fas-ligand double-deficient mice

Previously, we have shown that mice defective in granule exocytosis and/or Fas.L/Fas-mediated cytolytic pathways are significantly more resistant to alphavirus, Semliki Forest virus (SFV), infection compared with wild-type mice. Here, we evaluated SFV replication in different tissues of mice defective in both cytolytic pathways (perf−/−xgld) relative to that in wild-type counterparts and found that viral replication in perf−/−xgld mice is remarkably restricted. Although the mechanism responsible for this observation is yet to be established, the lower virus titres found in these mice indicate that the role of cytolytic effector molecules in antiviral immunity needs to be re-evaluated.

Exhaustion of type I interferon response following an acute viral infection

Viral infections often cause a period of heightened susceptibility to a secondary infection but the cause of this phenomenon is unknown. We found that a primary viral infection in mice rapidly triggers an IFN-I-dependent partial activation state in the majority of B and T lymphocytes, which reverts to a resting phenotype within 5 days. When a secondary infection with an unrelated virus occurred 5 to 9 days after the primary infection, no recurrence of marked activation of lymphocytes was observed. This was not due to an inherent inability of the previously activated cells to undergo renewed partial activation, because they responded when challenged with virus after transfer into "naive" recipients. Instead, the failure to respond optimally resided in the original host's incapacity to mount an IFN-I response to the secondary infection during this time period. Thus, transient immunosuppression through exhaustion of IFN-I production during an acute viral infection creates a time period of enhanced susceptibility to secondary infection.

NK cell-mediated immunopathology during an acute viral infection of the CNS

Natural killer (NK) and cytotoxic T (Tc) cells are prime effector populations in the antiviral response of the host. Tc cells are essential for recovery from many viral diseases but may also be responsible for immunopathology. The role of NK cells in recovery from viral infections is less well established. We have studied acute virulent Semliki Forest virus (vSFV) infection of the central nervous system in C57BL/6J mice, which was mainly controlled by NK cells without marked Tc cell involvement. We show that mice with defects in the Fas and/or granule exocytosis pathways of cytotoxicity are more resistant to lethal vSFV infection than wild-type mice. On the other hand, mice defective in the IFN-gamma response are more sensitive than wild-type mice, whereas mice lacking the Tc cell compartment (beta-2 microglobulin-deficient mice) exhibit susceptibility similar to wild-type mice. The additional finding that depletion of NK cells significantly delayed the mean time to death but did not prevent mortality in SFV-infected B6 mice suggests that cytolytic activity of NK cells is detrimental, while IFN-gamma production is beneficial for recovery from SFV infection. This is the first study illustrating an NK cell-mediated immunopathological outcome to an acute viral infection.

IL-15-independent antiviral function of primary and memory CD8+ T cells

Memory CD8⁺ T cells are comprised of CD122^hi IL-15-dependent and CD122^lo IL-15-independent subsets. Induction and retention of IL-15-independent memory CD8⁺ T cells was assessed in IL-15^−/− and wild-type (wt) mice immunized with recombinant vaccinia virus (rVV) or Sindbis virus (rSIN) vectors expressing the identical foreign epitope. Both vectors induced epitope-specific CD8⁺ T cell expansion and function, independent of IL-15. Similar kinetics of rVV clearance confirmed effective CD8⁺ T cell function in IL-15^−/− mice. CD44^hi CD122^hi CD8⁺ T cells, mainly of the CD62L^−/lo phenotype, increased more dramatically and declined more rapidly in IL-15^−/− mice, independent of the vector. Rapid IL-15-independent memory CD8⁺ T cell expansion following challenge of immune mice compensated for the limited memory CD8⁺ populations in IL-15^−/− mice. However, despite expansion and expression of potent effector function, viral clearance was delayed in the absence of IL-15, coinciding with a rapid loss in cytolytic function.

Maintenance of CD8(+) T-cell memory following infection with recombinant sindbis and vaccinia viruses

CD8(+) T-cell memory is critical for protection against pathogens poorly controlled by humoral immunity. To characterize two distinct vaccine vectors, the acute and memory CD8(+) T-cell responses to an HIV-1 epitope (p18) expressed by recombinant vaccinia (vp18) and Sindbis (SINp18) viruses were compared. Whereas 9 to 13% of CD8(+) splenocytes were p18 specific during the acute response to vp18, 4% were induced by SINp18 as revealed by class I tetramer staining. Increased T-cell activation by vp18 was confirmed by higher numbers of both p18-specific IFN-gamma-secreting splenocytes and activated CD8(+) and CD4(+) T cells. Although higher frequencies of p18-specific CD8(+) T cells during primary responses correlated with higher frequencies during memory, the overall decline was only two- to threefold during the transition to memory, demonstrating equally efficient maintenance of memory in SINp18- as in vp18-immune mice. Despite modest in vivo activation, SINp18-induced CD4(+) T cells secreted substantial amounts of IFN-gamma and IL-2, potentially contributing to sustained CD8(+) memory. Collectively the data indicate that Sindbis virus recombinants provide effective vaccines for inducing protective memory CD8(+) T cells in the absence of the extensive inflammation and replication associated with vaccinia virus.

Variation in the immune response to adenoviral vectors in the brain: influence of mouse strain, environmental conditions and priming

E1-deleted adenoviral vectors expressing the bacterial beta-galactosidase gene were inoculated into the brain of unprimed and primed C3H.He or C57BL/6J mice housed under either conventional or specific-pathogen-free (SPF) conditions. The kinetics of immune responses to both the vector and the transgene were investigated. In mice previously sensitized to adenovirus, the leukocyte infiltrate in the brain was dominated by CD8+ T cells, whereas in unprimed mice CD4+ T cells were present at higher levels. As expected, antibody titres to both adenovirus and beta-galactosidase were higher in primed mice than in unprimed mice after intracranial inoculation. C3H.He mice consistently made higher antibody responses than C57BL/6J mice. Although adenoviral vectors induced an inflammatory response under all conditions, mice housed in SPF facilities exhibited less inflammation than conventional mice and transgene expression persisted for longer. Irrespective of whether the mice had been deliberately primed to adenovirus, antibody titres were consistently lower in SPF mice compared with conventional mice. This study clearly demonstrates that environmental conditions, as well as previous priming to adenovirus, will affect both the quality and duration of the immune response triggered by gene delivery to the brain.

Alphavirus-specific cytotoxic T lymphocytes recognize a cross-reactive epitope from the capsid protein and can eliminate virus from persistently infected macrophages

Persistent alphavirus infections in synovial and neural tissues are believed to be associated with chronic arthritis and encephalitis, respectively, and represent likely targets for CD8+ alphabeta cytotoxic T lymphocytes (CTL). Here we show that the capsid protein is a dominant target for alphavirus-specific CTL in BALB/c mice and that capsid-specific CTL from these mice recognize an H-2Kd restricted epitope, QYSGGRFTI. This epitope lies in the highly conserved region of the capsid protein, and QYSGGRFTI-specific CTL were cross reactive across a range of Old World alphaviruses. In vivo the acute primary viraemia of these highly cytopathic viruses was unaffected by QYSGGRFTI-specific CTL. However, in vitro these CTL were able to completely clear virus from macrophages persistently and productively infected with the arthrogenic alphavirus Ross River virus.

Memory alloreactive cytotoxic T cells do not require costimulation for activation in vitro

We have studied the costimulation requirements for the generation of cytotoxic T (Tc) cells in an in vitro recall response to alloantigens. Firstly, we demonstrate that recombinant vaccinia viruses encoding class I MHC can stimulate primary in vivo responses and prime for secondary in vitro responses specific for the immunizing alloantigen. The secondary in vitro response comprises both naive and memory components that are distinguishable kinetically. Naive alloreactive Tc cell precursors are dependent upon the presence of CD80 on the in vitro stimulating population for activation and generation of effector function, as described previously. However, Tc cells from animals primed in vivo with vaccinia virus (VV) encoding allo-MHC do not require CD28-CD80 interactions to respond to the alloantigen presented in vitro. This finding provides further evidence that memory Tc cells have less stringent activation requirements in vitro than naive cells. From limiting dilution analysis of the relative contribution of naive and memory Tc cell precursors in 'primary' responses, to MHC class I alloantigen, memory alloreactive Tc cell precursors, possibly primed by cross-reactive environmental antigens, contribute approximately one-fifth of the precursors. Memory responses exhibit similar precursor frequencies as primary responses. Thus, we conclude that memory is largely a result of qualitative rather than quantitative changes in Tc cell precursors.

Flavivirus-induced up-regulation of MHC class I antigens; implications for the induction of CD8+ T-cell-mediated autoimmunity

Infection of a wide variety of cells of human, mouse and other species' origin by flaviviruses such as WNV, YF, Den, MVE, KUN and JE, increases the cell-surface expression of MHC class I. This MHC class I up-regulation is not due to increased MHC class I synthesis per se, but the result of increased peptide availability in the ER for MHC class I assembly. This is most likely due to the interaction of the viral polyprotein with the ER membrane during viral replication. Flavivirus infection can overcome peptide deficiency in TAP-deficient or non-permissive cell lines such as RMA-S and Syrian hamster cells, BHK and NIL-2. The consequence of this increased MHC class I expression manifests itself in reduced susceptibility to NK cells and augmented lysis by Tc cells. In mice, long-term flavivirus-immune Tc cell memory formation is impaired, following the appearance of strong anti-self Tc cell reactivity observed in in vitro cultures from splenocytes of flavivirus-primed animals. We hypothesize that flavivirus-induced MHC class I up-regulation leads to transient T-cell autoimmunity, followed by down-regulation of both autoimmunity and virus-specific Tc cell memory. Furthermore, we speculate that flavivirus infections of humans in the tropics may be responsible for the observed lower incidence of overt autoimmunity in these geographic regions than in temperate climates where flaviviruses are not endemic.

Aspects of cytotoxic T cell memory

Immunological T cell memory manifest itself in an accelerated second-set graft, or allogeneic tumour cell, rejection. Memory viral-immune cytotoxic T cells have shortened kinetics of induction in vivo and differentiate into more potent effector cells in vitro. The requirements for induction of memory T cells are less stringent than for naive T cells. Memory T cells can be activated by antigen (signal 1) or interaction with co-stimulatory molecules (CD28/CD80, signal 2) alone. Memory T cells are phenotypically distinguishable from naive T cells by a number of cell surface markers, but not from activated T cells. Persistence of antigen is not required for the maintenance of long-lived memory. Continuous stimulation by signal 2 alone and or longevity is sufficient to explain life-long persistence of T cell memory. All available data on memory T cells are consistent with a deterministic model of T cell memory formation, following a precise pathway of T cell differentiation.

Immunogens of encephalitis viruses

The equine encephalitis viruses are members of the genus Alphavirus, in the family Togaviridae. Three main virus serogroups represented by western (WEE), eastern (EEE) and Venezuelan equine encephalitis (VEE) viruses cause epizootic and enzootic infection of horses throughout the western hemisphere. All equine encephalitis viruses are transmitted through the bite of an infected mosquito. The first equine encephalitis virus vaccines were produced by virus inactivation. Problems with inadequate inactivation, which may have caused a major epidemic/epizootic of VEE in central America and Texas in the 1970s, led to the development of a live attenuated VEE virus vaccine (TC-83) derived by cell culture passage. Inactivated vaccines are still used to prevent equine infections with WEE and EEE viruses. Alphaviruses are small single stranded, positive sense RNA viruses. The 12000 nucleotide genome is enclosed in an icosahedral nucleocapsid composed of multiple copies of the capsid (C) protein. The virion is enveloped. The membrane is modified by the insertion of heterodimers of two glycoproteins: E1 and E2. Monoclonal antibody analysis of the surface glycoproteins have provided a detailed understanding of important protective antigens. Recent studies comparing gene sequences from virulent and avirulent VEE viruses have begun to delineate mechanisms of alphavirus attenuation.

Ir1 genes, peripheral cross-tolerance and immunodominance in MHC class I-restricted T-cell responses: an old quagmire revisited

Previous studies have shown that peripheral tolerance of one MHC molecule may influence the ability of an animal to respond to a particular antigenic determinant in the context of another MHC molecule (cross-tolerance). We describe here an investigation of the extent to which the presence of MHC molecules other than the one involved in Tc cell recognition affected whether or not a particular "antigen" (MHC/peptide) was recognized during the response of mice to infection with the flavivirus, West Nile (WNV). WNV-immune Tc cells from intra-H-2 recombinant mouse strains and F1 hybrid animals were used. In general, the antigens identified as immunogenic for five prototype mouse strains were immunogenic wherever the F1 or recombinant animal possessed the required MHC gene, but there were several notable exceptions. Firstly, while no responses were associated with Kd and Dk in BALB/c (H-2d) and CBA/H (H-2k) mice, respectively, in C3H.OH mice (Kd, Dk) both of these MHC molecules were associated with detectable responses. Secondly, in B10.A(2R) (Kk, Db) mice responses restricted by Db were not found whereas they were present in B6 mice (Kb, Db). This phenomenon was similar to previously reported phenomena with H-Y, Sendai, influenza and VV. However, it differed in two important ways. Firstly, we have no definitive evidence as yet that peripheral cross-tolerance to Kk influences responses against Db plus flavivirus as it does with H-Y and VV. Secondly, in addition to Kk, genes in the H-2s, H-2q and H-2d haplotypes influence responses to Db plus flavivirus but not responses to the other "antigens" listed above. Alternatively, the data are compatible with the concept of "immunodominance" based on a hierarchy of affinities of TCR's. the responding T-cell population appeared to focus the immune response on a limited number of "antigens"; in the presence of certain more strongly immunogenic "antigens", responses to other apparently more weakly immunogenic "antigens" were not seen.

Class I gene regulation of haplotype preference may influence antiviral immunity in vivo

The lymphocytic choriomeningitis virus (LCMV)-specific Tc response in (C3 X D2) F1 hybrids (k X d) is markedly biased in favor of the H-2d haplotype. Adoptive transfer experiments established that this haplotype preference also applied to T cell function in vivo. Using different mouse strain combinations we were unable to detect an influence of sex, non-H-2 background, maternal genotype, or route of priming on the preference pattern. In other haplotype combinations tested (k and b, b and d) no distinct haplotype preference was observed. A comparison of the LCMV-specific Tc response of (C X C3) F1 and (C-H-2dm2 X C3) F1 hybrids revealed that the dominance of the H-2d haplotype was controlled by H-2Ld. The ability of this gene to down-regulate the generation of an H-2k-restricted response did not seem to reflect antigenic mimicry since H-2k-restricted LCMV-specific Tc did not lyse H-2d expressing targets. In regard to the in vivo significance of haplotype preference it was found that (C X C3) F1 mice expressed an earlier and stronger virus-specific delayed type hypersensitivity response and exerted a more efficient virus control than did (C-H-2dm2 X C3) F1. Taken together these findings suggest that haplotype preference reflects a selection process favoring the restriction element associated with the most efficient immune response in vivo. The implications of this are discussed.

Differential target cell susceptibility to SFV-immune cytotoxic T-cells

Semliki Forest virus (SFV) infects a variety of murine cell types of H-2k haplotype. However, only L929 fibroblasts can be productively infected. Thioglycollate-induced peritoneal macrophages (TGM), and BW 5147 thymoma cells can be infected with SFV as demonstrated by SFV antigen expression on the cell surface and intracellularly. SFV-immune cytotoxic T (Tc) cells lyse only infected TGM and L929 target cells, however different times after infection are required for lysis of these two cell types. Split clone limiting dilution and cold target competition experiments are consistent with the interpretation that these two cell types display qualitatively different epitopes to SFV-immune Tc cells but do not exclude additional quantitative differences.

A region of the influenza A/NT/60/68 PB2 protein containing an antigenic determinant recognized by murine H-2Dd restricted cytotoxic T lymphocytes

We have used a recombinant vaccinia virus to investigate the recognition of the PB2 protein of influenza A/NT/60/68 (H3N2) by murine polyclonal CTL populations. PB2 is recognized as a major cross-reactive target antigen. Recognition of PB2 is under strict genetic control, since BALB/c (H-2d) but not CBA (H-2k) mice are responders. We also demonstrate, by use of cell lines transfected with individual genes encoding class I molecules of the H-2d haplotype, that recognition of PB2 occurs in conjunction with the H-2Dd but not the H-2Kd or H-2Ld molecules. In contrast, recognition of the nucleoprotein of A/PR/8/34 by BALB/c-derived polyclonal CTL is restricted via the H-2Kd molecule. By using three recombinant vaccinia viruses expressing deleted forms of the PB2 protein we show that at least one epitope of the PB2 protein resides within the amino-terminal 256 amino acids. This approach offers an effective method to map the regions of large proteins containing epitopes recognized by CTL.

T cell-mediated cytotoxicity against dengue-infected target cells

A cytotoxic T lymphocyte (CTL) response to dengue virus-infected target cells is described. Effector cells were generated in an in vitro secondary culture and appeared to be T cells possessing both the Lyt 1.1 and Lyt 2.1 surface antigens. A stronger CTL response was noted with the H-2k haplotype compared to H-2d, and H-2 compatibility was required between CTL and target cells. CTL generated showed some cross-reactivity with target cells infected with Japanese encephalitis virus (JEV), another flavivirus, but not with target cells infected with an alphavirus, Sindbis. The significance and importance of these findings are discussed.

The secondary in vitro murine cytotoxic T cell response to the flavivirus, West Nile

A secondary in vitro murine cytotoxic response to the flavivirus, West Nile (WNV) is described. Cytotoxic activity was obtained from spleen cells of mice primed 7 days previously with 10(6) p.f.u. WNV and boosted in vitro for a further 5 days with WNV-infected stimulator spleen cells. The cells responsible for lysis of WNV-infected target cells were restricted by class 1 H-2 antigens. The K region of the H-2k haplotype and both the K and D regions of the H-2d haplotype were permissive. The cytotoxic cells were virus-specific with respect to WNV and Influenza. The phenotype of the cells which mediated cytotoxicity was Thy 1+, Lyt 2+ and L3T4-; however an L3T4+ helper population was required for the optimal generation of the cytotoxic response in vitro.

Rotavirus-specific cytotoxic T lymphocytes cross-react with target cells infected with different rotavirus serotypes

Splenocytes from adult C57BL6 (H-2b) mice orally inoculated with nonmurine rotaviruses lysed syngeneic rotavirus-infected target cells. Cytotoxic T lymphocytes (CTLs) were responsible for this cytotoxic activity. Cytotoxic activity was (i) detected 7 days after primary oral inoculation; (ii) not detected in uninoculated animals; (iii) specific for rotavirus-infected target cells; (iv) eliminated by treatment with Thy 1.2-specific immunoglobulin M and complement; and (v) restricted at H-2Db. In addition, rotavirus-specific CTLs cross-reacted with target cells infected with different human or animal rotavirus serotypes. Heterotypic protection against rotavirus challenge may be mediated by cross-reactive CTLs.

Low responder MHC alleles for Tc recognition of influenza nucleoprotein

Since virus nucleoprotein is an important target antigen for anti-influenza cytotoxic T cells (Tc), we examined the genetics of Tc responses to this single viral protein to find three nonresponder alleles (Dd, Dk, and Kb) in three haplotypes and their recombinants so far tested. B10.A(5R) mice bearing nonresponder MHC class I antigen in the D and K regions show no anti-NP Tc responses, however they do show a strong A-virus cross-reactive anti-influenza cytotoxicity. The high frequency of nonresponsiveness to a single viral component, as compared with the entire virus, has implications for the development of simple vaccines.

In vitro secondary generation of cytotoxic T lymphocytes in mice with mumps virus and their mumps-specific cytotoxicity among paramyxoviruses

Murine cells (L929, MC57G, and P815 mastocytoma) defectively infected with the egg-adapted vaccine strain of mumps virus were found to be susceptible to cytotoxic T-lymphocyte (CTL)-mediated lysis. In vitro secondary, but not in vivo primary, generated CTL caused cytolysis of these targets in an H-2-restricted manner. UV-inactivated-mumps virus-coated murine cells were also found to be susceptible to CTL-mediated lysis. Comparisons of murine CTL-mediated lysis by three paramyxoviruses (mumps, Sendai, and Newcastle disease viruses) indicated that no cross-reactivity occurred. The CTL response with mumps virus exhibited specific unresponsiveness patterns, as influenced by the H-2 K/D regions of the mouse strains, that were partially different from those of Sendai virus and Newcastle disease virus.

Antibody responses in arthritic and uncomplicated Yersinia enterocolitica infections

Concentrations of antiyersinia antibody isotypes IgG1, IgG2, IgG3, IgG4, IgA and IgM were measured in 33 patients with yersiniosis using a solid-phase radioimmunoassay. Sixteen patients had a complicating reactive arthritis. Throughout the observation period IgG1 and IgM antibodies both constituted approximately one-third of the total antibodies, while IgA accounted for 10%, IgG3 accounted for 1%, and IgG4 antibodies could not be detected. IgG1, IgM, and IgA antibodies (and the total titer) had reached their peak at the beginning of the observation period (ca. day 20 after the onset of symptoms). The levels then gradually decreased; the total titers averaged 40 times the background at the beginning of the observation period and 4 times the background on day 350. IgM antibodies could be detected as late as a year after the infection. The concentration of IgG2 antibodies varied greatly from patient to patient. In most patients it increased until a plateau was reached approximately 2 months after the onset of symptoms. A decline was observed later. Five arthritic but no nonarthritic patients had a pronounced IgG2 response (more than half of the IgG antibodies were IgG2 in one or several samples).

Mouse serum as a medium supplement for murine immune responses in vitro

In vitro generation of secondary anti-viral H-2 restricted cytotoxic T cells (Tc cells) alloreactive Tc cells, alloantigen-induced T cell proliferation, bacterial lipopolysaccharide (LPS)-induced B cell proliferation and anti-dinitrophenyl IgM and IgG antibody responses were used to evaluate pools of mouse sera (MS) and other animal sera as medium supplements by comparison with 5-10% fetal calf serum (FCS). Some batches of normal MS were comparable with FCS while others inhibited Tc cell responses when used at 1%, particularly with limiting stimulator cell numbers. In contrast, 2 pools of nude mouse sera and several pools of MS from thioglycollate-injected mice (TMS) used at 1% were consistently comparable with FCS at 5-10% in terms of in vitro generation of effector Tc cells and antibody secreting B cells. TMS at 1% was satisfactory for Tc cell responses either fresh, after heat inactivation at 56 degrees C for 30 min, or after storage for 6 months at -70 degrees C. 0.5% or 2% heat-inactivated rat and rabbit sera (but not guinea pig sera) were also satisfactory for Tc cell generation. Total thymidine incorporation into proliferating B or T cells was 5-15-fold lower in cultures with 1% normal MS, nude MS or TMS than with 5% FCS, but stimulation indices with 1% nude MS and TMS were similar to those with 5% FCS, whereas 1% normal MS apparently completely inhibited stimulation. One percent syngeneic TMS is a convenient, reliable alternative to 5-10% FCS in culture medium, supporting all the murine responses listed above.

An improved colorimetric assay for T cell cytotoxicity in vitro

An improved colorimetric assay for estimation of cytotoxic T (Tc) cells is described. The method involves staining thioglycollate-induced macrophage targets with the dye neutral red prior to addition of cytotoxic T cells and estimating macrophage survival at the end of the assay by measuring dye remaining in viable targets. The method using macrophage targets is more sensitive than the 51Cr release assay employing macrophages or a variety of other targets. It may be used to detect alloreactive and H-2 restricted Tc cells in both short-term (4 h) and long-term (24 h) assays and overcomes some variability encountered with a previously described colorimetric procedure. Furthermore, the method is cheap, fast, reliable and avoids the use of radioactivity.

The immune response of the mouse to lymphocytic choriomeningitis virus. III. Differences of numbers of cytotoxic T lymphocytes in spleens of mice of different strains

By use of an accurate procedure for the measurement of relative numbers of murine cytotoxic T lymphocytes (CTL) marked differences of lymphocytic choriomeningitis virus-specific CTL in spleens were found among mouse strains that ranged from low over intermediate and high to very high, suggesting a gradient of responses rather than distinct classes. Differences were also found between mice sharing the major histocompatibility complex.

Automated colorimetric assay for T cell cytotoxicity

A colorimetric method has been developed for detecting the lysis of target cells by cytotoxic T lymphocytes (Tc). The method entails incubating Tc cells with thioglycollate-induced macrophage targets and estimating macrophage survival at the end of the assay by staining viable macrophages with the dye neutral red. The method is substantially more sensitive than the 51Cr release assay and can be used to detect alloreactive Tc cells and H-2-restricted Tc cells against viruses, haptens and minor-H antigens. Furthermore, the assay is applicable to limit dilution analysis of Tc cell precursors. The method is cheap, avoids radioactive materials and by measuring optical densities with automated spectrophotometers developed for microELISA systems, results can be obtained 50-100 times faster than with the radioactive procedure.

Equivalent decrease of H-2Kk and H-2Dk expression after vaccinia virus infection

Expression of H-2Kk and H-2Dk molecules was studied by indirect immunofluorescence on vaccinia virus-infected Ls cells (derived from the L929 cell line), using D-23b and ASA-21 monospecific alloantisera, respectively directed against the H-2.23 and H-2.32 private specificities of the H-2k haplotype. Our study demonstrates that the increase in vaccinia virus-induced antigens on the membrane of infected cells (as a function of the multiplicity of infection) is associated with a concomitant decrease in the expression of both H-2Kk and H-2Dk serologically defined private specificities. Absorption experiments of D-23b and ASA-21 sera, using infected or uninfected Ls cells, also indicate that after virus infection, H-2Kk and H-2Dk private specificities are equally altered in their serological expression. We finally show that this alteration consists in a mere quantitative decrease of H-2 molecules, since the cytolytic capacity of a rabbit anti-H-2 serum, specifically reacting against the constant part of the heavy chains of H-2 molecules, was significantly more absorbed by uninfected cells than by infected cells. We conclude that no preferential decrease in the expression of H-2 Kk and H-2 Dk molecules is induced during cell infection by vaccinia virus.

Variation of expression of histocompatibility antigens on tumor cells: absence of H-2Kk-gene products from a gross-virus-induced leukemia in BALB.K

The antigenic profile of the K-GV tumor of BALB.K origin, induced by Gross virus and maintained in vitro and in vivo, was investigated by serological and immunochemical methods and techniques of cell-mediated immunity. The H-2Kk-gene products were absent by several criteria: (1) monoclonal antibody and conventional alloantisera directed against eh H-2Kk antigenic specificities were nonreactive by direct testing and by absorptions. (2) H-2Kk products could not be precipitated from glycoprotein or protein extracts of the radiolabeled K-GV tumor. (3) Cytotoxic effectors against H-2Kk produced by sensitization in vitro and in vivo failed to kill K-GV target cells. (4) The tumor could neither stimulate BALB.B congenic mice to produce cytotoxic effectors nor specific cytotoxic antibody against H-2Kk-gene products. In contrast, the H-2Dk antigen was readily detectable by all these criteria. These findings therefore describe a tumor which has selectively lost the H-2K-gene products. The K-GV tumor was able to generate Gross-virus specific CTL, but had greatly reduced susceptibility to lysis by Gross-virus specific CTL generated by H-2K expressing AKR (H-2k) tumors. These findings have important implications for the associative recognition of tumor antigens and the immune surveillance of virally induced tumors.

Cross-reactive cytotoxic T cells to alphavirus infection

Secondary Tc cells immune to alphaviruses (BEB, SIN and SFV) cross-react between serologically defined subgroups at the level of target lysis and at the level of induction of response. Despite this apparently complete Tc cell cross-reactivity between BEB, SIN and SFV, antisera raised against BEB and SIN showed virus specificity in their ability to block Tc cell-mediated lysis of alphavirus-infected targets. This result suggests that Tc cells recognize the same viral antigen molecule as antibodies, but with less specificity. Other possible interpretations are discussed.