Characteristics of secondary cytotoxic T-cell responses in mice infected with influenza A viruses

Buccal and Sublingual Vaccines: A Review on Oral Mucosal Immunization and Delivery Systems

Currently, most vaccines available on the market are for parental use; however, this may not be the best option on several occasions. Mucosal routes of administration such as intranasal, sublingual, and buccal generate great interest due to the benefits they offer. These range from increasing patient compliance to inducing a more effective immune response than that achieved through conventional routes. Due to the activation of the common mucosal immune system, it is possible to generate an effective systemic and local immune response, which is not achieved through parenteral administration. Protection against pathogens that use mucosal entry routes is provided by an effective induction of mucosal immunity. Mucosal delivery systems are being developed, such as films and microneedles, which have proven to be effective, safe, and easy to administer. These systems have multiple advantages over commonly used injections, which are simple to manufacture, stable at room temperature, painless for the patient since they do not require puncture. Therefore, these delivery systems do not require to be administered by medical personnel; in fact, they could be self-administered.

Interferon-λ modulates dendritic cells to facilitate T cell immunity during infection with influenza A virus

Type III interferon (IFN-λ) is important for innate immune protection at mucosal surfaces and has therapeutic benefit against influenza A virus (IAV) infection. However, the mechanisms by which IFN-λ programs adaptive immune protection against IAV are undefined. Here we found that IFN-λ signaling in dendritic cell (DC) populations was critical for the development of protective IAV-specific CD8+ T cell responses. Mice lacking the IFN-λ receptor (Ifnlr1-/-) had blunted CD8+ T cell responses relative to wild type and exhibited reduced survival after heterosubtypic IAV re-challenge. Analysis of DCs revealed IFN-λ signaling directed the migration and function of CD103+ DCs for development of optimal antiviral CD8+ T cell responses, and bioinformatic analyses identified IFN-λ regulation of a DC IL-10 immunoregulatory network. Thus, IFN-λ serves a critical role in bridging innate and adaptive immunity from lung mucosa to lymph nodes to program DCs to direct effective T cell immunity against IAV.

The collagen binding alpha1beta1 integrin VLA-1 regulates CD8 T cell-mediated immune protection against heterologous influenza infection

A common feature of many infections is that many pathogen-specific memory T cells become established in diverse nonlymphoid tissues. A mechanism that promotes the retention and survival of the memory T cells in diverse tissues has not been described. Our studies show that the collagen binding alpha1beta1 integrin, VLA-1, is expressed by the majority of influenza-specific CD8 T cells recovered from nonlymphoid tissues during both the acute and memory phases of the response. Antibody treatment or genetic deficiency of VLA-1 decreased virus-specific CTL in the lung and other nonlymphoid tissues, and increased them in the spleen. In spite of the increase in the spleen, secondary heterosubtypic immunity against flu was compromised. This suggests that VLA-1 is responsible for retaining protective memory CD8 T cells in the lung and other tissues via attachment to the extracellular matrix.

Accessing complexity: the dynamics of virus-specific T cell responses

The cellular dynamics of the immune system are complex and difficult to measure. Access to this problematic area has been greatly enhanced by the recent development of tetrameric complexes of MHC class I glycoprotein + peptide (tetramers) for the direct staining of freshly isolated, antigen-specific CD8(+ )T cells. Analysis to date with both naturally acquired and experimentally induced infections has established that the numbers of virus-specific CD8(+) T cells present during both the acute and memory phases of the host response are more than tenfold in excess of previously suspected values. The levels are such that the virus-specific CD8(+) set is readily detected in the human peripheral blood lymphocyte compartment, particularly during persistent infections. Experimentally, it is now possible to measure the extent of cycling for tetramer (+)CD8(+) T cells during the acute and memory phases of the host response to viruses. Dissection of the phenotypic, functional, and molecular diversity of CD8(+) T cell populations has been greatly facilitated. It is hoped it will also soon be possible to analyze CD4(+) T cell populations in this way. Though these are early days and there is an enormous amount to be done, our perceptions of the shape of virus-specific cell-mediated immunity are changing rapidly.

Selection of CD8+ T Cells with Highly Focused Specificity During Viral Persistence in the Central Nervous System

The relationships between T cell populations during primary viral infection and persistence are poorly understood. Mice infected with the neurotropic JHMV strain of mouse hepatitis virus mount potent regional CTL responses that effectively reduce infectious virus; nevertheless, viral RNA persists in the central nervous system (CNS). To evaluate whether persistence influences Ag-specific CD8+ T cells, functional TCR diversity was studied in spleen and CNS-derived CTL populations based on differential recognition of variant peptides for the dominant nucleocapsid epitope. Increased specificity of peripheral CTL from persistently infected mice for the index epitope compared with immunized mice suggested T cell selection during persistence. This was confirmed with CD8+ T cell clones derived from the CNS of either acutely (CTLac) or persistently (CTLper) infected mice. Whereas CTLac clones recognized a broad diversity of amino acid substitutions, CTLper clones exhibited exquisite specificity for the wild-type sequence. Highly focused specificity was CD8 independent but correlated with longer complementarity-determining regions 3 characteristic of CTLper clonotypes despite limited TCR α/β-chain heterogeneity. Direct ex vivo analysis of CNS-derived mononuclear cells by IFN-γ enzyme-linked immunospot assay confirmed the selection of T cells with narrow Ag specificity during persistence at the population level. These data suggest that broadly reactive CTL during primary infection are capable of controlling potentially emerging mutations. By contrast, the predominance of CD8+ T cells with dramatically focused specificity during persistence at the site of infection and in the periphery supports selective pressure driven by persisting Ag.

The generation of memory antigen-specific cytotoxic T cell responses by CD28/CD80 interactions in the absence of antigen

The interaction of co-stimulatory molecules CD80/CD86 on antigen-presenting cells with CD28 on naive CD8+ cytotoxic T (Tc) cells is understood to be critical in the induction of Tc effectors. CD80 is capable of providing signal 2 for the activation of Tc cells, but has no effect if encountered in the absence of specific peptide/MHC complexes (signal 1). We have found that CD80 presented in vitro to resting memory viral-immune or alloimmune Tc cells can provide sufficient stimulus for the generation of effector Tc cells in the absence of specific antigen, the peptide/MHC class I complex. Effector Tc cells generated in vitro from influenza- or class I alloantigen-primed mice by co-stimulation in the absence of antigen require exogenous interleukin (IL)-2 signaling via the cell surface-expressed IL-2 receptor or, under conditions of IL-2 blockade, exogenous IL-7. Activation of memory Tc cells by signal 1 and 2 is independent of IL-2 and IL-7. Although memory influenza-immune Tc cells did respond to CD80 in the absence of antigen, the presence of antigen +CD80 enabled an earlier induction of these Tc cells and they retained their lytic activity in vitro over a longer time period. The capacity of memory Tc cells to be activated by signal 2 alone provides one explanation for the observed heterogeneity of phenotype of memory T cells in vivo and a possible mechanism for the maintenence of memory in the absence of persisting antigen.

Long-lived cytotoxic T lymphocyte memory in mucosal tissues after mucosal but not systemic immunization

The induction and maintenance of long-term CTL memory at mucosal surfaces may be a critical component of protection against mucosal pathogens and is one goal towards development of effective mucosal vaccines. In these studies we have functionally evaluated short and long-term CTL memory in systemic and respiratory or genital-associated lymphoid tissues following mucosal or systemic routes of immunization. Our results indicate that shortly after immunizing mice with a recombinant adenovirus vector expressing glycoprotein B (gB) of herpes simplex virus (AdgB8), gB-specific CTL memory responses were observed in systemic and mucosal immune compartments regardless of the route of inoculation. In contrast, several months after immunization, anamnestic CTL responses compartmentalized exclusively to mucosal or systemic lymphoid tissues after mucosal or systemic immunization, respectively. Furthermore, the compartmentalized CTL memory responses in mucosal tissues were functionally observed for longer than 1.5 yr after intranasal immunization, and CTL precursor frequencies one year after immunization were comparable to those seen shortly after immunization. Therefore, to our knowledge, this is the first functional demonstration that the maintenance of anti-viral memory CTL in mucosal tissues is dependent on the route of immunization and the time of assessment. These results have important implications for our understanding of the development, maintenance, and compartmentalization of functional T cell memory and the development and evaluation of vaccines for mucosal pathogens, such as HSV and HIV.

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.

Analysis of the cytolytic T-lymphocyte response to herpes simplex virus type 1 glycoprotein B during primary and secondary infection

The immune response to herpes simplex virus type 1 (HSV-1) infection in C57BL/6 mice includes a population of major histocompatibility complex class I-restricted cytolytic T lymphocytes (CTL) that recognize the structural glycoprotein gB. To gain insight into the importance of this CTL subpopulation in vivo, gB-specific CTL present in the regional lymph nodes after a primary infection and after a reinfection of convalescent animals were analyzed. In a primary infection, gB-specific CTL precursors (CTLp) that recognized either a cell line constitutively expressing gB or cells pulsed with the optimal Kb-restricted gB epitope 498SSIEFARL505 were present at an estimated frequency of 1/12,000 compared with a frequency of 1/3,000 for CTLp which recognized cells infected with HSV-1 itself. In convalescent mice responding to reinfection, HSV-specific CTLp were present at an estimated frequency of 1/4,000 to 1/14,000. However, gB-specific CTLp could not be detected at this site. These findings suggest that CTL specific for an immunodominant epitope contribute substantially to the primary response but may not be a component of the HSV-specific CTL population that responds rapidly to reinfection in vivo.

The long-term maintenance of cytotoxic T cell memory does not require persistence of antigen

I have used the transfer of primed lymphocytes into syngeneic irradiated recipients to investigate whether the persistence of antigen is required in the long-term maintenance of cytolytic T cell memory to influenza virus. Animals were immunized with influenza virus (A/WSN) and used 17 wk later as either donors for T cells or as lethally irradiated recipients. Naive age-matched mice served as controls. At intervals of 4, 8, 16, and 25 wk after T cell transfer, experimental and control groups were immunized with a heterologous virus (A/JAP) and splenocytes tested for lytic activity to influenza virus 3 and 6 d after immunization. Lytic activity 3 d after infection (a property exclusive to a memory cytotoxic T cell response) (Effros, R. B., J. Bennink, and P. C. Doherty. 1978. Cell. Immunol. 36:345.; and Hill, A. B., R. V. Blanden, C. R. Parrish, and A. Müllbacher. 1992. Immunol. Cell Biol. 70:259), was only observed by primed and naive irradiated recipients reconstituted with memory T cells. No day 3 responses were observed when naive T cells were transferred into irradiated primed or unprimed recipients. These observations demonstrate that cytolytic T cell memory to influenza virus is long lived in the absence of antigen.

In vivo administration of major histocompatibility complex class I-specific peptides from influenza virus induces specific cytotoxic T cell hyporesponsiveness

We have been investigating the immunogenicity of two class I major histocompatibility complex-specific peptides with a sequence derived from influenza virus nucleoprotein specific for Kd and one for Db. Peptide-modified splenocytes are unable to immunize for a primary cytotoxic T (Tc) cell response in vivo, or secondary response in vitro. Peptide-modified stimulator cells can boost virus-primed splenocytes for a strong secondary response in vitro. Animals primed with syngeneic peptide-modified splenocytes upon challenge with virus in vivo do not generate strong secondary Tc cell responses on day 3 after challenge in contrast to virus primed animals. Day 6 responses of virus-challenged, peptide-primed animals are reduced as compared to unprimed mice. This hyporesponsiveness is independent of CD8+ T cells in the priming population and can be elicited with tumor cell lines. The data are discussed in the framework of the two-signal model of immune induction.

Transfer of CD8+ T cells into SCID mice and activation of memory virus-specific cytotoxic T cells

The requirements for the activation of naive and memory CD8+ cytotoxic T (Tc) cells into effector virus-specific Tc cells after transferring them into SCID mice were investigated. SCID mice reconstituted with splenocytes or purified CD8+ T cells from naive or influenza-immune syngeneic mice and immunized with influenza virus generated effector Tc cells specific for influenza virus-infected target cells in vitro. The kinetics of the response varied between those two populations. The generation of effector Tc cells after transfer of memory CD8+ T cells indicates that there exists no absolute requirement for 'help' in the activation of memory virus-immune T cells. However, under the conditions described here the in vitro immunogenic peptide NPP derived from influenza nucleoprotein is not sufficient to elicit a response in vivo.

Restimulated memory Tc cells have a higher apparent avidity of interaction with targets than primary virus-immune Tc cells as indicated by anti-CD8 blocking

Previous experiments have shown that whereas a secondary in vitro Kunjin-immune cytotoxic T (Tc) cell population lysed equally well targets infected with either native flavivirus or a recombinant vaccinia virus expressing the immunodominant determinant, primary in vivo Kunjin-immune Tc cells were able to lyse only the recombinant vaccinia virus-infected targets. Using CD8 blockade to assess the avidity of T cell-target interaction, recombinant-infected targets express antigen more efficiently than native flavivirus infected targets and secondary in vitro Kunjin-immune Tc cells have a higher avidity for targets than do primary in vivo Kunjin-immune Tc cells. Secondary in vivo influenza-immune Tc cells are also of higher avidity than primary in vivo influenza-immune Tc cells. Thus, a restimulated memory Tc cell population interacts with targets with greater avidity than does a recently activated naive population.

Analyzing the distribution of cells expressing mRNA for T cell receptor gamma and delta chains in a virus-induced inflammatory process

Acute inflammatory processes are extremely complex, containing sets of activated cells that may be difficult to categorize. The interface between two methodologies for characterizing the involvement of gamma delta T cells, in situ hybridization to detect T cell receptor (TCR) mRNA and flow cytometric analysis of surface TCR expression, is utilized here to study the pneumonia caused by intranasal (i.n.) infection of mice with influenza A viruses. Substantial numbers of cells expressing mRNA for the gamma and delta TCR chains are present in bronchoalveolar lavage (BAL) populations obtained either late in the course of primary infection with an H3N2 virus or within a few days of secondary challenge with an H1N1 virus. The majority of the gamma delta TCR mRNA+ cells detected in FACS-separated BAL populations partition to the Thy1+ gamma delta TCR+ subset, while relatively few (less than 10%) C delta mRNA transcripts are found in cells that phagocytose latex particles. However, an additional set of gamma delta TCR mRNA+ cells is also located in a high side scatter (H-SSC) population, which stains nonspecifically with monoclonal antibodies (mAbs) and is normally gated out in the process of flow cytometric analysis. This H-SSC population tends to be enriched for cells expressing C gamma 1/2 rather than C gamma 4 mRNA. While some gamma delta TCR+ lymphocytes can be demonstrated by in vitro stimulation of the CD3 epsilon+ subset within this H-SSC population, the majority of the gamma delta T cell precursors that can be expanded in culture demonstrate a low side scatter (L-SSC) profile more characteristic of normal T lymphocytes. The possibility that subsets of activated, granular (H-SSC) alpha beta TCR+ and C gamma 1/2 mRNA+ gamma delta T cells are being missed when conventional FACS analysis is used to study this viral pneumonia is discussed.

Specific epitope-induced conversion of CD8+ memory cells into effector cytotoxic T lymphocytes in vitro: presentation of peptide antigen by CD8+ T cells

The requirements for the conversion of CD8+ memory T cells into effector class I major histocompatibility complex (MHC) Kd-restricted cytotoxic T (Tc) cells in vitro have been studied. Purified CD8+ splenocytes from influenza A/WSN-primed BALB/c (H-2d) mice stimulated with a synthetic nucleoprotein peptide 147-158 R156- (NPP) alone generated Tc cells specific for influenza virus-infected target cells. No additional requirements for accessory cells or their lymphokine products were necessary indicating that peptide antigen (Ag) in association with Kd was presented on CD8+ T cells. The evidence for presentation of NPP by CD8+ T cells was supported by the use of CD8+ memory T cells from semiallogeneic bone marrow radiation chimeras of P1----F1 type (H-2b----[H-2d x H-2b]F1). Memory CD8+ splenocytes from A/WSN-immune chimeras did not develop into secondary effector Tc cells as a result of a 4-day culture with NPP alone, however, were able to do so if NPP was presented by Kd-bearing Ag-presenting cells. In addition, these results exclude the possibility of direct recognition of free NPP molecules by the specific T cell receptor of CD8+ memory T cells. CD8+ memory splenocytes (H-2b) from chimeras were also able to develop into functionally active Tc cells as a result of presentation of Db-restricted synthetic peptide (NP 366-374) with a sequence derived from influenza virus nucleoprotein with high affinity for Db MHC class I molecules. Blockade of endogenously produced interleukin 2 (IL-2) activity by anti-IL-2 or anti-IL-2 receptor monoclonal antibody in the culture of CD8+ memory T cells during a 4-day NPP stimulation completely abolished Tc cell generation, indicating that the utilization of this lymphokine is absolutely required for the secondary Tc cell development. These findings demonstrate that CD8+ memory T cells per se are able to recognize the restimulating epitope as a result of its presentation by CD8+ T cells and develop into cytolytically active and highly specific Tc cells with no requirements for other cellular helper components or their lymphokine products.

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.

The generation and activation of memory class I MHC restricted cytotoxic T cell responses to influenza A virus in vivo do not require CD4+ T cells

The cellular requirements for the generation and activation of anti-influenza memory class I MHC restricted Tc cell responses were studied by selectively reconstituting lethally irradiated mice. The generation of memory Tc cells was investigated by using unprimed splenocytes to reconstitute infected, lethally irradiated mice; the activation of memory Tc cells was tested by using primed splenocytes to reconstitute uninfected, lethally irradiated mice. It is shown here that depletion of CD4+ T cells from donor cells did not reduce Tc cell responses in recipient mice. Depletion of CD8+ T cells from donor splenocytes prevented the memory Tc cell responses. Thus depletion of CD4+ T cells had no effect on the generation and activation of the memory Tc cells in vivo.

Homotypic and heterotypic immunity of influenza A viruses induced by recombinants of the cold-adapted master strain A/Ann Arbor/6/60-ca

The cold-adapted (ca) influenza A virus A/Ann Arbor/6/60-ca when administered intranasally to mice in two doses 3 weeks apart induces solid immunity to challenge 3 weeks later with heterotypic influenza A wild-type viruses (17). In the present study heterotypic immunity against viruses from different sub-types was shown to be relatively short-lived, having declined significantly 9 weeks after vaccination and being completely absent by 21 weeks. On the other hand, immunity against challenge viruses with surface antigens similar to the ca vaccinating virus or to other H 3 N 2 viruses remained high, even in the absence of detectable serum haemagglutination-inhibiting antibody. Both short- and long-term immunity induced by ca viruses was unaffected by earlier priming experiences with other wild-type or ca viruses. These results suggest that at least two mechanisms are involved in respiratory immunity to influenza viruses.

Cell-mediated cytotoxicity of peripheral blood mononuclear cells stimulated in vitro for infectious bovine rhinotracheitis virus-infected cells

Peripheral blood mononuclear cells (PBMC) from calves infected with and hyperimmunized to infectious bovine rhinotracheitis virus (IBRV) were stimulated in vitro with viral antigens to evaluate their cytotoxicity for a variety of cells. The 51-Cr release assay was used to measure cytotoxicity. Cytotoxicity was not present in fresh nonstimulated cells, but was detected in cultured, IBRV-stimulated cells at day 3, was maximal at day 7, and declined thereafter. PBMC stimulated in vitro with IBRV expressed a preference for killing IBRV-infected cells compared to pseudorabies virus (PRV)-infected cells. IBRV-infected, but not PRV-infected, cold target cells inhibited lysis of IBRV-labeled target cells. High concentrations of IBRV hyperimmune serum partially blocked cytotoxicity. Cells expressing a viral preference for cytotoxicity showed no preference for lysis of autologous compared to heterologous bovine cells. PBMC from calves that were either IBRV-immune or not immune were cultured without IBRV stimulation and had similar levels of cytotoxicity for IBRV-infected cells as cells from IBRV-infected cattle.

Rescue of anti-influenza A virus cytotoxic T-lymphocyte responses in chemotherapy-suppressed mice

The administration of cyclophosphamide (50 to 100 mg/kg) at 48 to 72 h before removal of murine lung or spleen mononuclear cells for culture rendered DBA/2 mice incapable of generating an effective cytotoxic T-lymphocyte response to influenza A virus-infected cells. The cytotoxic T-lymphocyte precursor frequency to influenza A virus in lung and spleen cells from cyclophosphamide-treated mice was significantly decreased when compared with that of normal littermate controls. The low cytotoxic T-lymphocyte activity in the lungs and spleens of cyclophosphamide-treated mice could be partially restored in vitro by human interleukin 2.

Killer T cell responses to influenza A during a drift period: studies in mice

After intravenous immunization of mice with any influenza A H3N2 drift strain attempts to restimulation of cytotoxic T cell (CTL) activities with the same virus or other drift period variants were unsuccessful for up to 6 weeks. Cross-stimulation 4-5 months after primary sensitization yielded, in most situations, positive but lower--as compared to primary--secondary cytotoxic T cell responses. Homotypic challenge was also effective after priming with some influenza A subtypes (A/E/72, A/PC/73, A/T/77) at this time.

Epitope specificity of the T cell proliferative response to lysozyme: proliferative T cells react predominantly to different determinants from those recognized by B cells

The fine specificity of murine B 10.A/SgSn (B 10.A) T cells reactive with hen egg-white lysozyme (HEL) has been studied through the use of reduced, carboxymethylated HEL, a set of peptides encompassing the entire molecule, and a set of variant lysozymes from other species. Cells were taken from the lymph nodes draining the site of immunization at the base of the tail, and were restimulated in vitro with immunogen or analogue to measure T cell reactivity. Unlike B cell reactivity, which we have shown to be mainly associated with an epitope preserved in the N-C peptide (residues 1--17, Cys6--Cys 127, 120--129) most T cell reactivity appears to be directed towards a limited number of determinants on cyanogen bromide cleavage fragment II of HEL (LII) (13--105). This was confirmed by a cell-dilution assay in which antigen-reactive units are measured; reactivity was highest to LII, intermediate to N-C, and low but significant to cyanogen bromide cleavage fragment III (LIII) (106--129). Furthermore, priming with LII is as effective as immunization with HEL and results in the same extensive cross-reactivities to variant lysozymes. Although LII reactivity predominates in the response to HEL, injection of LIII and N-C reveals sizeable reactivity to the homologous peptides and to HEL. By cross-stimulation studies, specific epitopes could be defined in certain regions of HEL. B 10.A is clearly responsive to the overlap between N-C and LII (residues 13--17), and to an epitope in the region 106--121, but is poorly responsive to the C-terminal portion (120--129). The response to 106--121 is characterized by an exquisite specificity in which as little as a single amino acid substitution (Asn for Gln) is recognized.

Natural and immune cytolysis of canine distemper virus-infected target cells

Natural and immune cytolysis of canine distemper virus (CDV)-infected target cells in vitro is described. Lymphocytes expressing natural cytotoxicity were found in specific-pathogen-free beagle dogs and in beagle-coonhound crosses before vaccination with CDV and indefinitely after vaccination, when the ephemeral immune lymphocyte-mediated cytotoxicity (ILMC) had declined. In contrast to the natural lymphocyte-mediated cytotoxicity, the ILMC was genetically restricted, could not be blocked by CDV-specific antibody, and was effective against measles virus-infected as well as CDV-infectd target cells. Lymphocyte populations were depleted of Fc receptor and surface immunoglobulin-bearing cells by rosetting techniques and tested in comparison. An antibody-dependent cell-mediated cytotoxicity was demostrated against CDV-infected target cells that were preincubated with CDV antibody when Fc receptor-bearing lymphocytes were not removed. The ILMC was measurable for approximately 10 days beginning at 6 days post-vaccination. In contrast, CDV antibody measured by virus neutralization and humoral cytotoxicity was detectable by 6 days postvaccination and persisted at peak levels for at least 5 months.

Recognition of viral glycoproteins by influenza A-specific cross-reactive cytolytic T lymphocytes

Two populations of cytolytic T lymphocytes (CTL) generated after influenza A virus infection can be distinguished into one with specificity for the sensitizing hemagglutinin type and a second with cross-reactivity for antigens induced by other type-A influenza viruses. The molecules carrying the antigenic determinants recognized by the cross-reactive CTL were studied. In L-929 cells abortively infected with fowl plague virus, matrix (M) protein synthesis is specifically inhibited, whereas the envelope glycoproteins, hemagglutinin and neuraminidase, are synthesized and incorporated into the plasma membrane. These target cells were lysed by cross-reactive CTL. The envelope proteins of type A/Victoria virus were separated from the other virion components and reconstituted into lipid vesicles that lacked M protein that subsequently were used to prepare artificial target cells. Target-cell formation with vesicles was achieved by addition of fusion-active Sendai virus. These artificial target cells were also susceptible to lysis by cross-reactive CTL. In contrast to previous observations that suggested that the M protein of influenza viruses is recognized by these effector cells, we present evidence that the antigencic determinants induced by the viral glycoproteins are recognized.

Influenza virus-specific T cell-mediated cytotoxicity: integration of the virus antigen into the target cell membrane is essential for target cell formation

This study deals with the requirements for target cell recognition by influenza A virus-specific cytotoxic T lymphocytes (CTL). H-2-identical cells were incubated with infectious or UV light-inactivated influenza A virus expressing either cleaved or uncleaved hemagglutinin (HA). Thereafter, the treated cells were tested in a 4-h 51Cr assay for susceptibility to CTL-mediated cytolysis. Regardless whether the influenza virus was infectious, virions expressing cleaved HA were efficient in target cell formation. In contrast, cells incubated with either active or UV-inactivated virions expressing uncleaved HA were not lysed by virus-specific CTL. Yet, after mere trypsin-mediated cleavage of the HA of cell-absorbed viroins, strong cytolysis could be observed. On the other hand, solubilization of the envelope lipid bilayer by ethylether abolished the capacity of the remaining HA to induce target cell formation. The results clearly suggest that mere absorption of virions to the membrane of cells, which is performed by virus with uncleaved HA, is insufficient for target cell formation. For this, both cleaved HA and an intact envelope appear to be crucial. We conclude that fusion of the virion into the cell membrane is essential for target cell formation.