Role of T-cell function in recovery from murine influenza infection

Epitope screening and self-assembled nanovaccine molecule design of PDCoV-S protein based on immunoinformatics

Based on the whole virus or spike protein of pigs, δ coronavirus (PDCoV) as an immunogen may have unrelated antigenic epitope interference. Therefore, it is essential for screening and identifying advantageous protective antigen epitopes. In addition, immunoinformatic tools are described as an important aid in determining protective antigenic epitopes. In this study, the primary, secondary, and tertiary structures of vaccines were measured using ExPASy, PSIPRED 4.0, and trRosetta servers. Meanwhile, the molecular docking analysis and vector of the candidate nanovaccine were constructed. The immune response of the candidate vaccine was simulated and predicted using the C-ImmSim server. This experiment screened B cell epitopes with strong immunogenicity and high conservation, CTL epitopes, and Th epitopes with IFN-γ and IL-4 positive spike proteins. Ferritin is used as a self-assembled nanoparticle element for designing candidate nanovaccine. After analysis, it has been found to be soluble, stable, non-allergenic, and has a high affinity for its target receptor, TLR-3. The preliminary simulation analysis results show that the candidate nanovaccine has the ability to induce a humoral and cellular immune response. Therefore, it may provide a new theoretical basis for research on coronavirus self-assembled nanovaccines. It may be an effective candidate vaccine for controlling and preventing PDCoV.

Viral T-cell epitopes - Identification, characterization and clinical application

T-cell immunity, mediated by CD4⁺ and CD8⁺ T cells, represents a cornerstone in the control of viral infections. Virus-derived T-cell epitopes are represented by human leukocyte antigen (HLA)-presented viral peptides on the surface of virus-infected cells. They are the prerequisite for the recognition of infected cells by T cells. Knowledge of viral T-cell epitopes provides on the one hand a diagnostic tool to decipher protective T-cell immune responses in the human population and on the other hand various prophylactic and therapeutic options including vaccination approaches and the transfer of virus-specific T cells. Such approaches have already been proven to be effective against various viral infections, particularly in immunocompromised patients lacking sufficient humoral, antibody-based immune response. This review provides an overview on the state of the art as well as current studies regarding the identification and characterization of viral T-cell epitopes and approaches of clinical application. In the first chapter in silico prediction tools and direct, mass spectrometry-based identification of viral T-cell epitopes is compared. The second chapter provides an overview of commonly used assays for further characterization of T-cell responses and phenotypes. The final chapter presents an overview of clinical application of viral T-cell epitopes with a focus on human immunodeficiency virus (HIV), human cytomegalovirus (HCMV) and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), being representatives of relevant viruses.

Using Adjuvants to Drive T Cell Responses for Next-Generation Infectious Disease Vaccines

Using adjuvants to drive features of T cell responses to vaccine antigens is an important technological challenge in the design of new and improved vaccines against infections. Properties such as T helper cell function, T cell memory, and CD8+ T cell cytotoxicity may play critical roles in optimal and long-lived immunity through vaccination. Directly manipulating specific immune activation or antigen delivery pathways with adjuvants may selectively augment desired T cell responses in vaccination and may improve the effectiveness and durability of vaccine responses in humans. In this review we outline recently studied adjuvants in their potential for antigen presenting cell and T cell programming during vaccination, with an emphasis on what has been observed in studies in humans as available.

Modelling cross-reactivity and memory in the cellular adaptive immune response to influenza infection in the host

The cellular adaptive immune response plays a key role in resolving influenza infection. Experiments where individuals are successively infected with different strains within a short timeframe provide insight into the underlying viral dynamics and the role of a cross-reactive immune response in resolving an acute infection. We construct a mathematical model of within-host influenza viral dynamics including three possible factors which determine the strength of the cross-reactive cellular adaptive immune response: the initial naive T cell number, the avidity of the interaction between T cells and the epitopes presented by infected cells, and the epitope abundance per infected cell. Our model explains the experimentally observed shortening of a second infection when cross-reactivity is present, and shows that memory in the cellular adaptive immune response is necessary to protect against a second infection.

Natural T Cell-mediated Protection against Seasonal and Pandemic Influenza. Results of the Flu Watch Cohort Study

RATIONALE

A high proportion of influenza infections are asymptomatic. Animal and human challenge studies and observational studies suggest T cells protect against disease among those infected, but the impact of T-cell immunity at the population level is unknown.

OBJECTIVES

To investigate whether naturally preexisting T-cell responses targeting highly conserved internal influenza proteins could provide cross-protective immunity against pandemic and seasonal influenza.

METHODS

We quantified influenza A(H3N2) virus-specific T cells in a population cohort during seasonal and pandemic periods between 2006 and 2010. Follow-up included paired serology, symptom reporting, and polymerase chain reaction (PCR) investigation of symptomatic cases.

MEASUREMENTS AND MAIN RESULTS

A total of 1,414 unvaccinated individuals had baseline T-cell measurements (1,703 participant observation sets). T-cell responses to A(H3N2) virus nucleoprotein (NP) dominated and strongly cross-reacted with A(H1N1)pdm09 NP (P < 0.001) in participants lacking antibody to A(H1N1)pdm09. Comparison of paired preseason and post-season sera (1,431 sets) showed 205 (14%) had evidence of infection based on fourfold influenza antibody titer rises. The presence of NP-specific T cells before exposure to virus correlated with less symptomatic, PCR-positive influenza A (overall adjusted odds ratio, 0.27; 95% confidence interval, 0.11-0.68; P = 0.005, during pandemic [P = 0.047] and seasonal [P = 0.049] periods). Protection was independent of baseline antibodies. Influenza-specific T-cell responses were detected in 43%, indicating a substantial population impact.

CONCLUSIONS

Naturally occurring cross-protective T-cell immunity protects against symptomatic PCR-confirmed disease in those with evidence of infection and helps to explain why many infections do not cause symptoms. Vaccines stimulating T cells may provide important cross-protective immunity.

HLA targeting efficiency correlates with human T-cell response magnitude and with mortality from influenza A infection

Experimental and computational evidence suggests that HLAs preferentially bind conserved regions of viral proteins, a concept we term "targeting efficiency," and that this preference may provide improved clearance of infection in several viral systems. To test this hypothesis, T-cell responses to A/H1N1 (2009) were measured from peripheral blood mononuclear cells obtained from a household cohort study performed during the 2009-2010 influenza season. We found that HLA targeting efficiency scores significantly correlated with IFN-γ enzyme-linked immunosorbent spot responses (P = 0.042, multiple regression). A further population-based analysis found that the carriage frequencies of the alleles with the lowest targeting efficiencies, A*24, were associated with pH1N1 mortality (r = 0.37, P = 0.031) and are common in certain indigenous populations in which increased pH1N1 morbidity has been reported. HLA efficiency scores and HLA use are associated with CD8 T-cell magnitude in humans after influenza infection. The computational tools used in this study may be useful predictors of potential morbidity and identify immunologic differences of new variant influenza strains more accurately than evolutionary sequence comparisons. Population-based studies of the relative frequency of these alleles in severe vs. mild influenza cases might advance clinical practices for severe H1N1 infections among genetically susceptible populations.

Assessing mathematical models of influenza infections using features of the immune response

The role of the host immune response in determining the severity and duration of an influenza infection is still unclear. In order to identify severity factors and more accurately predict the course of an influenza infection within a human host, an understanding of the impact of host factors on the infection process is required. Despite the lack of sufficiently diverse experimental data describing the time course of the various immune response components, published mathematical models were constructed from limited human or animal data using various strategies and simplifying assumptions. To assess the validity of these models, we assemble previously published experimental data of the dynamics and role of cytotoxic T lymphocytes, antibodies, and interferon and determined qualitative key features of their effect that should be captured by mathematical models. We test these existing models by confronting them with experimental data and find that no single model agrees completely with the variety of influenza viral kinetics responses observed experimentally when various immune response components are suppressed. Our analysis highlights the strong and weak points of each mathematical model and highlights areas where additional experimental data could elucidate specific mechanisms, constrain model design, and complete our understanding of the immune response to influenza.

MHC class I-presented T cell epitopes identified by immunoproteomics analysis are targets for a cross reactive influenza-specific T cell response

Influenza virus infection and the resulting complications are a significant global public health problem. Improving humoral immunity to influenza is the target of current conventional influenza vaccines, however, these are generally not cross-protective. On the contrary, cell-mediated immunity generated by primary influenza infection provides substantial protection against serologically distinct viruses due to recognition of cross-reactive T cell epitopes, often from internal viral proteins conserved between viral subtypes. Efforts are underway to develop a universal flu vaccine that would stimulate both the humoral and cellular immune responses leading to long-lived memory. Such a universal vaccine should target conserved influenza virus antibody and T cell epitopes that do not vary from strain to strain. In the last decade, immunoproteomics, or the direct identification of HLA class I presented epitopes, has emerged as an alternative to the motif prediction method for the identification of T cell epitopes. In this study, we used this method to uncover several cross-specific MHC class I specific T cell epitopes naturally presented by influenza A-infected cells. These conserved T cell epitopes, when combined with a cross-reactive antibody epitope from the ectodomain of influenza M2, generate cross-strain specific cell mediated and humoral immunity. Overall, we have demonstrated that conserved epitope-specific CTLs could recognize multiple influenza strain infected target cells and, when combined with a universal antibody epitope, could generate virus specific humoral and T cell responses, a step toward a universal vaccine concept. These epitopes also have potential as new tools to characterize T cell immunity in influenza infection, and may serve as part of a universal vaccine candidate complementary to current vaccines.

Immunoinformatic comparison of T-cell epitopes contained in novel swine-origin influenza A (H1N1) virus with epitopes in 2008-2009 conventional influenza vaccine

In March 2009 a novel swine-origin influenza A (H1N1) virus (S-OIV) emerged in Mexico and the Western United States. Vaccination with conventional influenza vaccine (CIV) does not result in cross-reactive antibodies, however, the disproportionate number of cases (37%) occurring among persons younger than 50 years old suggested that adaptive immune memory might be responsible for the relative lack of virulence in older, healthy adults. Using EpiMatrix, a T-cell epitope prediction and comparison tool, we compared the sequences of the three hemagglutinin (HA) and neuraminidase (NA) proteins contained in 2008-2009 CIV to their counterparts in A/California/04/2009 (H1N1) looking for cross-conserved T-cell epitope sequences. We found greater than 50% conservation of T helper and CTL epitopes between novel S-OIV and CIV HA for selected HLA. Conservation was lower among NA epitopes. Sixteen promiscuous helper T-cell epitopes are contained in the S-OIV H1N1 HA sequence, of which nine (56%) were 100% conserved in the 2008-2009 influenza vaccine strain; 81% were either identical or had one conservative amino acid substitution. Fifty percent of predicted CTL epitopes found in S-OIV H1N1 HA were also found in CIV HA sequences. Based on historical performance, we expect these epitope predictions to be 93-99% accurate. This in silico analysis supports the proposition that T-cell response to cross-reactive T-cell epitopes, due to vaccination or exposure, may have the capacity to attenuate the course of S-OIV H1N1 induced disease-in the absence of cross-reactive antibody response. The value of the CIV or live-attenuated influenza vaccine containing the 2008-2009 vaccine strains, as defense against H1N1, could be further tested by evaluating human immune responses to the conserved T-cell epitopes using PBMC from individuals infected with H1N1 and from CIV vaccinees.

Control of mucosal virus infection by influenza nucleoprotein-specific CD8+ cytotoxic T lymphocytes

Background

MHC class I-restricted CD8⁺ cytotoxic T lymphocytes (CTL) are thought to play a major role in clearing virus and promoting recovery from influenza infection and disease. This has been demonstrated for clearance of influenza virus from the lungs of infected mice. However, human influenza infection is primarily a respiratory mucosal infection involving the nasopharynx and tracheobronchial tree. The role of CD8⁺ CTL directed toward the influenza nucleoprotein (NP) in defense against influenza virus infection at the respiratory mucosa was evaluated in two separate adoptive transfer experiments.

Methods

Influenza nucleoprotein (NP)-specific CD8⁺ CTL were generated from splenocytes obtained from Balb/c mice previously primed with influenza A/Taiwan/1/86 (H1N1) infection or with influenza A/PR/8/34 (H1N1)-derived NP plasmid DNA vaccine followed by infection with A/Hong Kong/68 (H3N2) virus. After in vitro expansion by exposure to an influenza NP-vaccinia recombinant, highly purified CD8⁺ T cells exhibited significant lysis in vitro of P815 target cells infected with A/Hong Kong/68 (H3N2) virus while the CD8^- fraction (CD4⁺ T cells, B cells and macrophages) had no CTL activity. Purified CD8⁺ and CD8^- T cells (1 × 10⁷) were injected intravenously or interperitoneally into naive mice four hours prior to intranasal challenge with A/HK/68 (H3N2) virus.

Results

The adoptively transferred NP-vaccinia-induced CD8⁺ T cells caused significant reduction of virus titers in both the lungs and nasal passages when compared to CD8^- cells. Neither CD8⁺ nor CD8^- T cells from cultures stimulated with HIV gp120-vaccinia recombinant reduced virus titers.

Conclusion

The present data demonstrate that influenza NP-specific CD8⁺ CTL can play a direct role in clearance of influenza virus from the upper respiratory mucosal surfaces.

Cellular Immunity and Lung Injury in Respiratory Virus Infection

Respiratory virus infection may result in considerable lung injury, and host immune responses may be an important contributor to this. Important factors that determine the magnitude of immunopathologic tissue damage include the degree of distal distribution of infection into alveolar cells, the overall viral load, the magnitude of the T-cell responses, the effector mechanisms employed by the T cells, and regulatory mechanisms which may come into play. CD8+ T cells are important contributors to viral clearance, utilizing contact-dependent effector functions (perforin and CD95L) as well as IFN-gamma and TNF-alpha. IFN-gamma and TNF-alpha are primary perpetrators of T-cell-mediated lung injury, with TNF as the major contributor. It is not entirely clear at present the degree to which injury is a necessary consequence of host defense to respiratory virus infection, though there are tantalizing bits of evidence to the contrary. In murine models, TNF plays only a minor role in antiviral activity and clearance of laboratory strains of RSV and influenza. In the event of a pandemic with a highly virulent virus, intervention directed at TNF-alpha should be given consideration, as this may be most likely to provide protection against severe lung injury at the lowest cost to viral clearance.

The immune system provides a strong response to even a low exposure to virus

How influenza virus dose affects the size of the immune response has not been clearly documented. Mice were challenged with three doses of influenza virus spanning a 100-fold range. Increasing the viral input dose increased the degree of weight loss observed, the clinical score and eventual mortality. Maximum viral loads increased with viral input and lower doses peaked and declined earlier. The level of the immune response only varied 2-fold and was independent of viral dose with near maximal responses elicited by the lowest dose, as measured by influx of antigen-specific and non-specific leukocytes into the lungs and by influenza antibody titers. We conclude that a strong immune response is mounted to a small dose of virus and curbs the spread of virus early and prevents weight loss whereas larger doses of virus elicit a slightly greater response but the associated disease can overwhelm the host.

Discrimination of resident and infiltrated alveolar macrophages by flow cytometry in influenza A virus-infected mice

Laser flow cytometric analysis was used in conjunction with in vivo labeling with the lipophilic fluorescent dye DiIC18(5)-DS to discriminate resident alveolar macrophages from newly infiltrating monocytes/macrophages in mice with and without pulmonary influenza A virus infection. Leukocytes in bronchoalveolar lavage (BAL) and peripheral blood were analyzed by 2-color flow cytometry as a function of time following intravenous injection of DiIC18(5)-DS. At 4 hours, dye-positive leukocytes were present in both BAL and blood of normal mice, indicating that DiIC18(5)-DS rapidly crossed the pulmonary endothelial-epithelial barrier. At 4 days after dye injection, 98% of BAL cells were DiIC18(5)-DS positive, and almost all of these were monocytes/macrophages based on labeling with fluorescein isothiocyanate (FITC)-conjugated antibody to the Mac-3 marker. Only 3.2% +/- 0.3% of peripheral blood monocytes (approximately 0.16% of total peripheral blood leukocytes) were DiIC18(5)-DS positive at 6 days after injection, whereas > 95% of BAL leukocytes were strongly dye-positive on days 6 to 28. When DiIC18(5)-DS was injected in mice 6 days prior to intranasal challenge with influenza A, flow cytometry indicated that 57.8% 5.6% and 60.7% +/- 8.5% of macrophages/monocytes in BAL were newly infiltrated (i.e., DiIC18(5)-DS negative, Mac-3 positive) at 4 and 7 days, respectively, post viral infection. The discrimination of subpopulations of resident and newly recruited macrophages in BAL should facilitate future mechanistic studies on pulmonary infection and inflammatory lung injury.

The unmet need in the elderly: Designing new influenza vaccines for older adults

Influenza is a serious illness and probably the single most important cause of excess disability and mortality during the winter months. In spite of limited efficacy in older adults, influenza vaccination is nevertheless a cost-saving medical intervention since it does reduce hospitalisation and death rates due to pneumonia, exacerbations of heart failure and, surprisingly, heart attacks and strokes. Yet hospitalisation and death rates for acute respiratory illnesses continue to rise in spite of widespread vaccination programs. As a person ages, the immune response to antigenic stimulation with the influenza virus shifts toward T helper type 2 cytokine production. This is associated with a relative reduction in cytotoxic T-cell activity and a reduced capacity to destroy infected host cells and clear the virus from infected lung tissue. Breakthrough strategies to improve the current influenza vaccines are required to avoid a crisis in health care. A targeted approach will develop vaccines that can reverse these age-related changes in T-cell responses, particularly the functions of cytotoxic T lymphocytes.

Specific history of heterologous virus infections determines anti-viral immunity and immunopathology in the lung

Having previously shown that previous immunity to one virus can influence the host response to a subsequent unrelated virus, we questioned whether the outcome to a given virus infection would be altered in similar or different ways by previous immunity to different viruses, and whether immunity to a given virus would have similar effects on all subsequent infections. In mouse models of respiratory viral infections, immunity to lymphocytic choriomeningitis virus (LCMV), murine cytomegalovirus (MCMV), or influenza A virus enhanced both Th1-type cytokine responses and viral clearance in the lung on vaccinia virus infection. A common pathological feature was the presence of chronic mononuclear infiltrates instead of the acute polymorphonuclear response seen in the infected nonimmune mice, but some pathologies such as enhanced bronchus-associated lymphoid tissue and bronchiolitis obliterans were unique for the immunizing virus, LCMV. Immunity to influenza virus influenced subsequent infections diversely, inhibiting vaccinia virus but enhancing LCMV and MCMV titers and completely altering cytokine profiles. Influenza virus immunity enhanced the mild mononuclear responses usually observed during acute infections with MCMV or LCMV in nonimmune mice, but unique features such as enhanced bronchiolization and mononuclear consolidation occurred during MCMV infection of influenza virus-immune mice. Heterologous immunity induced two patterns of disease outcome dependent on the specific virus infection sequence: improved, if the acute response switched from a neutrophilic to a lymphocytic response or worsened, if it switched from a mild to a severe lymphocytic response. Heterologous immunity thus occurs between many viruses, resulting in altered protective immunity and lung immunopathology, and this is influenced by the specific virus infection sequence.

Peptide-based synthetic recombinant vaccines with anti-viral efficacy

Synthetic recombinant vaccines are constructs in which a synthetic oligonucleotide coding for a protective epitope is inserted into an adequate gene for expression of the epitope. We report the results obtained using recombinant flagella of Salmonella vaccine strain expressing epitopes of influenza virus or of the parasite Schistosoma mansoni. In the case of influenza virus, three conserved epitopes of the haemagglutinin and the nucleoprotein of the virus inducing B- and T-cell immune response, were expressed and the flagella were used for intranasal immunization without any adjuvant. Both humoral and cellular immune responses specific to the virus induced in mice cross-strain long-term protection against challenge infection. Aged mice were also able to resist infection. For the design of a human influenza vaccine, epitopes recognized by the HLAs prevalent in Caucasian populations were used, and the resulting vaccine was evaluated in human/mouse radiation chimaera in which human PBMC are functionally engrafted. The vaccinated mice demonstrated efficient clearance of the virus after challenge and resistance to lethal infection. In the case of the parasitic disease schistosomiasis, a 14-residue peptide denoted 9B peptide 1 was expressed in the flagella. Intranasal vaccination of mice with this construct, without the use of adjuvant, resulted in 40% protection against challenge infection.

Perforin-independent CD8(+) T-cell-mediated cytotoxicity of alveolar epithelial cells is preferentially mediated by tumor necrosis factor-alpha: relative insensitivity to Fas ligand

CD8(+) T cells appear to play an important pathophysiologic role in many inflammatory lung diseases. The primary effector function of this T-cell subset is cytolysis of virus-infected cells, and it is widely believed that there are two primary molecular mechanisms by which this occurs: the perforin/granzyme-mediated pathway of cytolysis, and the Fas ligand (FasL)-Fas (CD95/APO-1) pathway of induction of target-cell apoptosis. This conclusion is based primarily on data obtained with hematopoetic cell lines as target cells. There is also a growing body of evidence that Fas is involved in the transduction of apoptotic signals in a variety of inflammatory disease states, particularly involving the liver and the lung. In the study reported here we took advantage of a novel in vitro assay to directly assess the effector mechanisms employed in CD8(+) T-cell-mediated cytolysis of alveolar epithelial cells. We present evidence that FasL-induced, Fas-mediated apoptosis does not directly contribute to T-cell-mediated cytolysis of alveolar epithelial-derived cells, even though Fas is expressed and functional on these cells. We also demonstrated that the perforin-independent cytolytic activity of CD8(+) T cells against alveolar epithelial-derived cells is explained entirely by tumor necrosis factor-alpha (TNF-alpha), which is expressed on CD8(+) T cells. Furthermore, we show that bystander cytolysis of alveolar epithelial-derived cells by antiviral CD8(+) T cells is entirely perforin-independent. This activity is mediated exclusively by TNF-alpha. Both alveolar epithelial-derived cells and primary murine type II cells show susceptibility to apoptosis triggered by soluble TNF-alpha, without the need for transcriptional or translational inhibition. We also confirmed the resistance of alveolar type II cells to FasL in vivo by performing adoptive transfer of perforin-deficient antiviral CD8(+) T cells into transgenic mice expressing a target antigen in type II epithelial cells. Significant lung injury developed in the transgenic CD8(+) T-cell recipients, whether or not Fas was expressed in these animals. Furthermore, preincubation of the T cells with antibody to TNF-alpha completely abolished the injury. These results suggest that alveolar epithelial cells are relatively sensitive to T cell-triggered, TNF-alpha-mediated apoptosis, and resistant to apoptosis triggered by FasL. These observations may have important ramifications for understanding of the pathophysiology of interstitial and inflammatory lung diseases.

Time course of the porcine cellular and humoral immune responses in vivo against pseudorabies virus after inoculation and challenge: significance of in vitro antigenic restimulation

We investigated the time course of porcine cellular and humoral immune responses against pseudorabies virus (PRV) after pigs were inoculated with PRV gE(-) mutant strain M141 and challenged with wild-type virus NIA-3. Peripheral blood mononuclear cells (PBMC) were isolated from blood samples; half were used directly and half were restimulated with PRV in vitro before use in a cytolytic assay. We determined time course and extent of PRV-specific lymphoproliferative and cytolytic response. In addition, serum samples were examined for neutralizing antibodies. After inoculation, the frequency of various lymphocyte subsets in peripheral blood was determined by FACScan. One week after inoculation, T-lymphocytes proliferated abundantly and a B-lymphocyte response was observed. When PBMC were used directly without restimulation, only 15% of the PRV-infected target cells were lysed, and about 15-20% of uninfected target cells were lysed. In contrast, when PBMC were restimulated with PRV, up to 50% of the PRV-infected target cells were lysed while only 30% of the uninfected target cells were lysed. The frequency of various T-lymphocyte subsets in the circulation did not change significantly after inoculation, which indicates that the number of PRV-specific lymphocytes in circulation was very small. After challenge, the T-lymphocyte response was enhanced, but the B-lymphocyte response was not. When PBMC were used directly, only 20% of the PRV-infected and uninfected target cells were lysed after challenge. In contrast, when PBMC were restimulated with PRV, they again lysed more PRV-infected target cells than uninfected target cells. Cytolytic cells were detected for a longer period after challenge than after inoculation. Since it was only possible to clearly detect cytolysis after lymphocytes were restimulated with PRV, it may be that they do not preferentially localize in blood or that they are too few in blood to be detected without further antigenic restimulation in vitro. These lymphocytes may instead localize in other tissues, such as mucosal tissues, tonsils and draining lymph nodes. Whether such a reservoir of PRV-specific cytolytic cells is important in clearing the virus is still unknown. In this study we demonstrated PRV-specific lymphocytes in circulation after they were restimulated in vitro with PRV.

Antibody response to influenza immunization in patients after heart transplantation

The aim of this study was to evaluate post-heart transplantation (Htx) response to two-dose and three-dose influenza vaccine. Hemagglutination inhibition antibodies were monitored in HTx recipients immunized twice (n = 25) or three times (n = 17), and non-HTx controls (n = 8) once, with inactivated influenza vaccine. Post-first dose protective antibody titers (> or = 1:40) were demonstrated in 9/25 (36%) for A/Singapore/ (H1N1), 5/25 (20%) for A/Shanghai/(H3N2) and 2/25 (8%) for B/Yamagata compared with 4/8 (50%), 6/8 (75%) and 2/8 (25%), respectively, for controls. Post-second dose protective titers remained low, increasing following the third dose to 71%, 65% and 29%, respectively. The abnormally low antibody responses of HTx recipients to one-dose and two-dose influenza vaccine can be overcome by a third dose.

Granzyme B independently of perforin mediates noncytolytic intracellular inactivation of vesicular stomatitis virus

Cytotoxic cells provide a crucial defense against DNA and RNA viral infections. Here we describe an in vitro model to study the fate of vesicular stomatitis virus (VSV) RNA in cells undergoing apoptosis. Using the [3H]uridine release assay, we show that human LAK cells induce the degradation of RNA in infected U937 cells in addition to inhibiting the production of infectious virions. LAK cell-mediated RNA degradation was blocked by the serine protease inhibitor, 3,4-dichloroisocoumarin. Purified human granzyme B but not inactivated granzyme B, granzyme A, or perforin rapidly induced degradation of RNA in VSV-infected U937 cells in a dose- and time-dependent manner without lysing the cells and suppressed viral production. Northern analysis of RNA extracted from infected cells with a VSV full-length cDNA probe confirmed that levels of viral transcripts were reduced by treatment with granzyme B. Nevertheless, the amount of host beta-actin mRNA was also reduced in infected cells, suggesting that treatment with granzyme B induced apoptosis. Consistent with this notion, infected cells exposed to granzyme B rapidly developed DNA strand breakage. Taken together, the data suggest that granzyme B in the absence of perforin reduced VSV production by activating a mechanism that degraded viral transcripts in infected U937 cells.

Characteristics of the intrahepatic cytotoxic T lymphocyte response in chronic hepatitis C virus infection

Based on our CTL studies of over 44 persons with chronic HCV infection, we are able to arrive at a number of conclusions. Clearly this cellular immune response is heterogeneous among infected persons. We have not identified any specific HCV protein which appears to be immunodominant for CTL responses, but rather we have detected diverse responses to both structural and non-structural proteins. Using an identical stimulation strategy for all persons studied, we have been able to detect responses in only approximately one third of persons with chronic infection. Among these persons, the responses among liver-infiltrating lymphocytes are greater than those detected in fresh peripheral blood, suggesting that the CTL are homing to the site of maximal viral burden in these persons. Some viral proteins contain overlapping epitopes presented by more than one HLA class I molecule, and we have also found cases where peptides in the same HLA superfamily, such as the HLA A3 superfamily which contains A11, for which the same peptide can be presented by both alleles (manuscript in preparation). Although sequence variation between the infecting strain and the vaccinia constructs used to test for responses may lead to non-recognition of some variants, even the highly conserved core protein appears to be an inconsistent and actually infrequent target for detectable CTL responses. The magnitude of the CTL response appears to vary greatly, from being undetectable to being so vigorous that it an be detected in stimulated peripheral blood. The breadth of the response also varies widely, ranging from the detection of a response to a single epitope in some persons, to the simultaneous recognition of up to five different epitopes in others. Even in persons of the same HLA type, we have not seen consistent targeting of the same epitopes except in rare cases. Despite the detection of over 20 epitopes and their restricting class I alleles using CTR derived from liver-infiltrating lymphocytes, we have identified only one epitope that has been shown to be targeted by more than one person of the same HLA type. These findings lead us to speculate that the CTL response may be submaximal in the majority of infected persons. The reasons for this are presently obscure, but could relate to a number of factors. The epitopes targeted are found within variable regions of the virus, such that immune escape from established CTL responses has to be considered a real possibility. Sequence variation may also lead to antagonism of CTL responses, as has been demonstrated for both HIV and HBV infections. Furthermore, sequence variation either within or adjacent to regions containing CTL epitopes can lead to altered antigen processing, either due to alteration of proteolytic processing of the viral peptides in the cytoplasm or to altered transport and altered association with class I molecules. A number of issues regarding the CTL response in HCV infection still require substantial attention. The apparent inability of CTL to clear this virus needs to be addressed, as does the potential role for viral immunomodulatory molecules in HCV persistence. Although we and others have shown CTL responses to be present in persons with chronic infection, the role of CTL in acute HCV infection needs to be determined. The best studied chronic human viral infection is HIV infection, in which expanding data indicate that the early events following primary infection predict the subsequent course of illness. Viral load in the first 1-2 years after infection is highly predictive of the subsequent disease course in HIV infection, and recent experimental data in humans suggest that early immune responses may be predictive of subsequent disease course. Such studies in HCV infection have been difficult to achieve, since primary HCV infection is often asymptomatic, and transfusion-related cases are now rare. (ABSTRACT TRUNCATED)

Twenty years into the saga of MHC-restriction

Twenty years ago, the terms 'altered self' and 'H-2 restriction', later modified to 'MHC-restriction', were coined to describe the finding by Peter Doherty and Rolf Zinkernagel that murine cytotoxic T cells (CTL) would lyse virus-infected target cells only if effector and target cells were H-2 compatible. This short review recalls those heady days and briefly recounts some of the later findings in three aspects of particular interest raised by the original finding: the nature of the T cell receptor, the composition and structure of the ligand on the target cell recognized by the TCR and the importance of CTL in the control and clearance of infections in general.

Influenza virus-specific CD4+ T helper type 2 T lymphocytes do not promote recovery from experimental virus infection

T lymphocytes play a primary role in recovery from viral infections and in antiviral immunity. Although viral-specific CD8+ and CD4+ T cells have been shown to be able to lyse virally infected targets in vitro and promote recovery from lethal infection in vivo, the role of CD4+ T lymphocytes and their mechanism(s) of action in viral immunity are not well understood. The ability to further dissect the role that CD4+ T cells play in the immune response to a number of pathogens has been greatly enhanced by evidence for more extensive heterogeneity among the CD4+ T lymphocytes. To further examine the role of CD4+ T cells in the immune response to influenza infection, we have generated influenza virus-specific CD4+ T cell clones from influenza-primed BALB/c mice with differential cytokine secretion profiles that are defined as T helper type 1 (Th1) clones by the production of interleukin 2 (IL-2) and interferon gamma (IFN-gamma), or as Th2 clones by the production of IL-4, IL-5, and IL-10. Our studies have revealed that Th1 clones are cytolytic in vitro and protective against lethal challenge with virus in vivo, whereas Th2 clones are noncytolytic and not protective. Upon further evaluation of these clonal populations we have shown that not only are the Th2 clones nonprotective, but that pulmonary pathology is exacerbated as compared with control mice as evidenced by delayed viral clearance and massive pulmonary eosinophilia. These data suggest that virus-specific CD4+ T cells of the Th2 subset may not play a primary role in virus clearance and recovery and may lead to immune mediated potentiation of injury.

Response to influenza infection in mice with a targeted disruption in the interferon gamma gene

Interferon gamma (IFN-gamma) is a pleiotropic cytokine secreted by T lymphocytes and natural killer (NK) cells and has been noted to be a first line of host defense in the control of viral infections. To examine further the role of this cytokine in the control of viral infections, mice with a targeted mutation in the IFN-gamma gene were infected with influenza virus, and the in vivo antibody and cell-mediated immune response to viral infection were examined. In addition, cell lines and clones were derived from the immunized animals and the in vitro cytokine production and cytotoxic T lymphocyte (CTL) response were analyzed. The absence of IFN-gamma led to increased production of influenza-specific IgG1, IL-4, and IL-5 as compared to wild-type littermate control animals. In contrast, there was no difference noted in the development of an effective CTL response between IFN-gamma-deficient and wild-type animals. In this model of experimental influenza infection, IFN-gamma is not necessary for the development of an effective humoral or cellular immune response to challenge with this respiratory virus.

Recombinant vaccine vector-induced protection of athymic, nude mice from influenza A virus infection. Analysis of protective mechanisms

Athymic, nude mice, which normally succumb to virus infection, can resolve infection with recombinant vaccinia virus (rVV) engineered to express IL-2. We have demonstrated that interferon-gamma (IFN-gamma) produced by natural killer (NK) cells and other immunocytes in response to the virus-encoded interleukin-2 (IL-2) is crucial to recovery. Here, we extend this work to show that nude mice, when primed intravenously with rVV co-expressing both IL-2 and an influenza virus haemagglutinin (HA) gene, are also protected following challenge with a lethal dose of homologous influenza virus. A substantial increase in the number of influenza virus-reactive antibody-secreting cells producing antibody of the IgM isotype, but not of the IgG or IgA isotypes, was found in spleens and lungs of the protected mice. Treatment with monoclonal antibodies to IFN-gamma or to the NK marker, as GM1, at challenge and thereafter, led to their death however, though the specific IgM antibody response was unaffected. These data suggest that both specific antibody and non-specific antiviral reactivity are important elements of the protective response and show that this immunization strategy may be used to protect severely immunocompromised individuals.

Murine infection by vesicular stomatitis virus: initial characterization of the H-2d system

BALB/c mice and congenic H-2Ld-deficient BALB/c-H-2dm2 (dm2) mice were experimentally infected intranasally with isolates of vesicular stomatitis virus (VSV). The survival of infected hosts, viral replication in lungs and brains, and histopathologic in the two mouse strains were compared. In both strains of mice, mortality occurred during the period 7 to 10 days postinfection. However, dm2 mice were relatively resistant to lethal infections. Viral replication occurred at low levels in the lungs of both strains and did not evoke significant pathologic changes. In contrast, viral replication in the brains was much greater; in the BALB/c strain, this was accompanied by more frequent and more severe pathologic changes. In general, mice surviving at day 10 had effectively cleared virus from central nervous system but not respiratory sites. Evidence is presented that viral replication occurs first in the nasal cavity and is transmitted both to the lungs and to the olfactory bulb where focal cytopathology occurs. Virus enters the ventricles, causing encephalitis; necrosis occurs around the ventricles and in the lumbosacral region of the spinal cord. Necrotic lesions were accompanied by mononuclear infiltration. Mice immunized with virus of the same serotype or with a vaccinia virus hybrid encoding the VSV glycoprotein were protected from lethal infection; in contrast, mice immunized with heterotypic virus were susceptible to challenge.

Interferon gamma is involved in the recovery of athymic nude mice from recombinant vaccinia virus/interleukin 2 infection

Athymic nude mice recover from an infection with recombinant vaccinia virus (VV) encoding murine interleukin 2 (IL-2), but treatment with a mAb to IL-2 accentuated infection. Administration of a mAb against interferon gamma (IFN-gamma) to mice infected with the IL-2-encoding virus completely prevented the IL-2-induced mechanisms of recovery. Both asialo-GM1+ (NK) and asialo-GM1- (non-NK) cells were participants in the IFN-gamma-mediated recovery of nude mice from infection with the IL-2-encoding VV recombinant. Depletion of asialo-GM1+ cells exacerbated infection, though not as much as anti-IFN-gamma mAb. In vitro, both asialo-GM1+ and asialo-GM1- nude mouse splenocytes produced IFN-gamma in response to IL-2.

The roles of influenza virus haemagglutinin and nucleoprotein in protection: analysis using vaccinia virus recombinants

Vaccinia virus recombinants expressing haemagglutinin (HA) or nucleoprotein (NP) from influenza virus A/PR/8/34 were used to investigate protective immunity in mice, with two protocols. Protection was assessed by mortality and morbidity rates and by lung virus titres after infection intranasally with A/PR/8/34. In the first protocol, mice immunized with vaccinia-HA recombinant virus and infected intranasally with A/PR/8/34 were almost totally protected, but mice immunized with vaccinia-NP virus were very poorly protected. In the second protocol, the recombinant viruses were used to stimulate in vitro T cells that are specific for HA and NP; both populations of T cells, when transferred to A/PR/8/34-infected mice, afforded good protection. The results indicate that an immune response specific for just HA provided protection that was almost indistinguishable from that provided by whole A/PR/8/34. On the other hand, immunization with vaccinia-NP provided poor protective immunity, despite the fact that transferred NP-specific T cells were very effective and vaccinia-NP immunization has previously been shown to stimulate cytotoxic T cells. These results demonstrate that a single viral antigen, delivered by live vaccinia virus, can provide effective protection, but that immunization for cross-protection against heterologous influenza virus remains elusive.

Temporal regulation of influenza hemagglutinin expression in vaccinia virus recombinants and effects on the immune response

Regulation of the expression of influenza A/PR/8/34 hemagglutinin (HA) by the vaccinia virus promoters PF (early), P7.5 (early and late) and PL11 (late) has been demonstrated using HA-vaccinia recombinant viruses VV-PR8-HA3, VV-PR8-HA6 and VV-PR8-HA, respectively. Levels of HA on the surface of VV-PR8-HA3 (PF)-infected cells were lower than with either VV-PR8-HA6 (P7.5) or VV-PR8-HA8 (PL11). Expression of HA under the control of the late promoter PL11 was inhibited in the absence of DNA replication. All three recombinant viruses stimulated a specific antibody response in mice which was dependent on the presence of infectious virus. Recognition of HA by cytotoxic T lymphocytes (CTL) was assessed by the ability of the viruses to stimulate naive precursors in vivo, to restimulate primed CTL in vitro and by target cell recognition. HA expressed under the control of either of the promoters with early function (PF or P7.5) was recognized by CTL when VV-PR8-HA3 or VV-PR8-HA6 were used to prime or restimulate splenocytes or to infect target cells. On the other hand, HA expressed by VV-PR8-HA8 (PL11) failed to prime for a CTL response in naive CBA/H mice, was ineffective at restimulation of primed splenocytes and failed to produce target cells for recognition by specific CTL. However, in BALB/c mice VV-PR8-HA8 did prime for a specific CTL response. These studies show that HA synthesized early in infection was recognized by both B and T cells while HA expressed after DNA replication was not generally recognized by T cells. The implications of the observations with the late promoter with respect to the use of late promoters in potential vaccinia virus-based vaccines are considered.

Functional analysis of influenza-specific helper T cell clones in vivo. T cells specific for internal viral proteins provide cognate help for B cell responses to hemagglutinin

We compared the effects of adoptively transferred Th cell clones specific for the influenza hemagglutinin (HA), matrix (M), or nucleoprotein (NP) on the antibody response of nude mice infected with A/PR/8/34 influenza virus. We show that the production of antibodies to the HA absolutely requires the presence of virus-specific Th cells. Further, transfer of a Th clone specific for the internal proteins, M or NP, was as effective as was transfer of an HA-specific clone in supporting an antibody response to the HA. With each of the clones, the kinetics of the response were accelerated by approximately 3 d compared with the antibody response of normal BALB/c mice. The HA- and M-specific clones supported an isotype switch from IgM to IgG and IgA similar to that which occurs during a normal antibody response. Finally, as shown by coinfection experiments, the response required a cognate T-B interaction whether the determinants recognized by the Th and B cell are located on the same viral protein or on different viral proteins within the same virus particle. The implications of these findings for understanding the T-B interactions that occur during an effective antiviral antibody response are discussed.

Nonspecific influx of cytotoxic T cells into influenza virus-infected lungs of mice

The influx of cytotoxic T cells into A/WSN influenza virus-infected mouse lungs was investigated by adoptive transfer with [125I] 5-iodo-2'-deoxyuridine ([125I]UdR)-labeled syngeneic cells. More A/WSN virus-immune secondary effector T cells were localized in the A/WSN virus-infected lungs than in the uninfected lungs, the ratios being in the range 2.5-5.0 Nonimmune control cells, in contrast, showed no significant difference in the localization pattern in infected compared to uninfected lungs. Virus-immune T cells of different antigenic specificities, i.e., Sendai or Semliki Forest virus-immune secondary effector T cells, however, also localized more in A/WSN virus-infected than in uninfected lungs, but the heterologous virus-immune T cells were retained in the A/WSN virus-infected lungs for a shorter time than A/WSN virus-immune secondary effector T cells. The work suggests mechanisms other than antigenic specificity may be important in the localization of immune T cells in virus-infected lungs.

Mechanism of recovery from acute virus infection. III. Subclass of T lymphocytes mediating clearance of lymphocytic choriomeningitis virus from the spleens of mice

Spleen T lymphocytes from mice undergoing acute infection with lymphocytic choriomeningitis virus (LCM virus) were negatively selected by treatment with anti-Lyt or anti-L3T4 antibodies and complement. The subsets thus obtained were tested for their potential to lyse LCM virus-infected target cells in vitro and to confer on infected syngeneic recipients the ability to eliminate virus rapidly from their spleens. Both capacities were found to be associated with Lyt-1-2+, L3T4- cells. Previous studies had shown that LCM virus-specific cytotoxicity in vitro as well as reduction of replication of LCM virus in the adoptively immunized mouse requires compatibility at K and/or D of the major histocompatibility complex, and we conclude that clearance of LCM virus from the mouse's spleen is mediated by the subset of T lymphocytes that is functionally characterized as cytotoxic/suppressive.

In vivo effects of cyclosporine on influenza A virus-infected mice

Cyclosporine (cyclosporin A, CsA) administered to mice substantially affects their immune response to an influenza A virus infection. If treated with CsA for 21 days, the mouse lungs contain high titers of virus which are cleared more slowly than in controls. Indicators of pathological damage--lung weight, extent of consolidation, fine morphology, and the extent of infiltration of dividing cells into the lung--showed that administration of CsA greatly decreased the level of inflammation. The production of hemagglutination-inhibiting (HI) antibody was delayed but reached almost control levels and NK cell activity in the lung was also comparable to control levels. In contrast, a delayed-type hypersensitivity (DTH) response to the virus could not be elicited in the CsA-treated, infected mice at 6 or 12 days after infection. Cytotoxic-T-cell (Tc-cell) activity was present in the lungs of such mice though its appearance was delayed and the activity recovered was less than that of the control infected mice. If administered with a dose of virus lethal for normal mice. CSA-treated mice survived, probably due to the greatly reduced level of immunopathological damage in the infected lung.

Enhanced resistance of mice against influenza virus infection after local administration of glycoprotein extracts from Klebsiella pneumoniae

RU. 41 740, a glycoprotein extract from Klebsiella pneumoniae O1K2 strain was tested for its ability to enhance resistance of mice against influenza virus infection. Local (aerosol) and systemic (IP) routes of RU. 41 740 administration were compared for their effectiveness in protecting mice. When RU. 41 740 was administered prophylactically (10 mg/kg) via aerosol route (5 consecutive days before challenge), significant protection (P less than 0.0001) was conferred against lethal aerosol inoculation of influenza virus. Treated mice exhibited a reduced mortality, a decreased lung-to-body weight ratio and lower intrapulmonary virus titers. The main glycoprotein soluble fraction (RU. 41 821) was as active as the total glycoprotein extract (P less than 0.0001). Whereas the local (aerosol) route of administration was effective, the systemic (intraperitoneal) route of administration did not confer significant protection against an aerosol inoculum of virus. This finding suggests the important role of local immunity. The levels of interferon in the lavage fluids of immunized and infected mice suggest that interferon is not the main protective mechanism. The enhanced protection observed could be related to an augmented humoral or cell-mediated response within the lung.

In vivo effector function of influenza virus-specific cytotoxic T lymphocyte clones is highly specific

Cloned lines of murine cytotoxic T lymphocytes (CTL) directed to type A influenza virus confer complete protection upon adoptive transfer to syngeneic mice lethally infected by influenza virus. The exquisite specificity exhibited by a subtype-specific cloned CTL in culture is reflected in its capacity to eliminate pulmonary virus and mediate recovery only in those mice infected by the virus subtype recognized by this cloned line in vitro. A cross-reactive CTL cloned line protects mice infected by either of two influenza virus subtypes. In mice dually infected with two virus subtypes, the subtype-specific CTL clone only reduces lung virus levels of the recognized virus subtype and cannot prevent these mice from dying. In contrast, adoptive transfer of the cross-reactive CTL clone into mice simultaneously infected with two virus subtypes results in reduction of pulmonary titers of both subtypes and promotes complete recovery. These results directly implicate CTL as an important antiviral defense mechanism in experimental influenza infection. In addition, these results indicate that both the induction and expression of antiviral effector activity by CTL in vivo is highly specific and therefore favor the concept that CTL express their antiviral effect in vivo by direct cytolysis of infected cells.

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.

Cytotoxic T lymphocyte recognition of the influenza hemagglutinin gene product expressed by DNA-mediated gene transfer

We have used the technique of DNA-mediated gene transfer to examine cytotoxic T lymphocyte (CTL) recognition of the product of the cloned A/JAPAN/305/57 hemagglutinin (HA) gene in murine (L929) cells. Using both heterogeneous and homogeneous (clonal) populations of type A influenza-specific CTL, we have demonstrated that the HA molecule can serve as a target antigen for both the subtype-specific and the cross-reactive subpopulations of influenza-specific CTL. Our results also raise the possibility that other virus-specified polypeptides may serve as target molecules for cross-reactive CTL.

Activity of cyclosporin A in experimental influenza virus infection in mice

Oral administration of the immunosuppressive fungal metabolite cyclosporin A increased the mortality of Balb/c mice infected intranasally with influenza A/Hong Kong/1/68 (H3N2) virus. Cyclosporin A also increased the amount of virus that could be recovered from the lungs of infected mice and delayed the rate at which it was eliminated. Treatment with cyclosporin A did not, however, prevent the appearance of haemagglutination inhibiting antibody in the sera of animals that had been infected with a sub-lethal concentration of virus.

The generation of 'cytotoxic' macrophages in mice during infection with influenza A or Sendai virus

Injection of infectious but not of non-infectious influenza A virus or of infectious or non-infectious Sendai virus intraperitoneally into mice induces the generation of plastic-adherent cells that are able to effect release of 51Cr from labelled virus-infected target cells but not from labelled, uninfected cells. Their activity is greatly diminished by exposure to silica or carrageenan but not by anti-Thy 1 antibody and complement treatment. Similarly, the activity of the cell preparation cannot be explained by contamination with natural killer or 'K' cells. Thus, the effector cells were identified as macrophages and for convenience are called 'cytotoxic macrophages'. The maximum cytotoxic activity was recovered from the peritoneal cavity 5 days after virus injection and declined thereafter. Although the effector cells are cross-reactive in that cells activated by an influenza A strain virus lyse target cells infected with the same or other A strain viruses or with Sendai virus, there is preferential lysis of cells infected with the homologous virus. The action of the effector cells is not h-2-restricted. Preliminary experiments showed that similar effector cells can be recovered from the lungs of mice 5 days after intranasal inoculation of infectious influenza virus, so they may contribute to the host control of the disease.

Induction of natural killer cells during murine influenza virus infection

Cells which are cytotoxic for both virus-infected and uninfected target cells can be recovered from the spleens of mice injected with either infectious or non-infectious influenza A virus. Peak activity doccurs at 1-2 days and decreases to low levels by day 6. The effector cells are insensitive to anti-Thy 1 antibody and complement treatment, are not H-2 restricted, do not adhere to plastic and are unaffected by silica or carrageenan. in this sense and in the pattern of susceptibility to lysis of a variety of cultured cell lines, these effector cells have the properties of natural killer (NK) cells and are referred to as such. They are present to an increased level of activity in nude (nu+/nu+) mice and to a low level of activity in beige (bg+/bg+) mice, but upon injection of virus there is a significant increase in activity in both hosts. Such cells were also recovered from the lungs of mice infected intranasally with a lethal or sublethal dose of virus. In the former case, maximum activity was reached 2 days post infection and the activity remained high until death; in the latter case, peak activity was reached 4 days after virus inoculation and by day 11 the activity had decreased to pre-infection levels. After intranasal inoculation of influenza virus, both beige mice and their heterozygous littermates contained similar levels of infectious virus in their lungs. However, this result does not eliminate the possibility that these cells may help to limit virus infection.

Antibodies to the strain-specific and cross-reactive determinants of the haemagglutinin of influenza H3N2 viruses. Antiviral activities of the antibodies in biological systems

Antibodies to the strain-specific (SS) and cross-reactive (CR) antigenic determinants of the haemagglutinin (HA) of influenza H3N2 viruses were prepared, and their antiviral properties in experimentally infected mice and in eggs were investigated. The SS antibodies were considerably more efficient than the CR antibodies in direct virus neuralization tests. The difference in the activities of the two types of antibody preparations was less pronounced in virus growth inhibition studies in the allantois-on-shell system and in passive protection studies in mice give antibody before challenge with virus. Nevertheless, even in these tests SS antibody was approximately four-fold more effective than was CR antibody in protection against fatal infection. Passive administration of CR or SS antibody preparations to mice challenged with sublethal virus doses, reduced the peak pulmonary titres of virus on day three post-infection compared with the control animals. The degree of reduction in titre exerted by the SS antibodies was greater than for the CR antibodies. In contrast, the rate of clearance of pulmonary virus 9-12 days after infection in the mice treated with SS antibody was slower than for the CR treated animals. Also, in SS antibody treated animals viruses isolated from mouse lungs showed evidence of minor antigenic variation away from the parent virus.

Specificity, Ly phenotype, and H-2 compatibility requirements of effector cells in delayed-type hypersensitivity responses to murine influenza virus infection

Delayed-type hypersensitivity (DTH) to infectious and to noninfectious (UV-irradiated) influenza A viral preparations was measured in mice by the increase in footpad swelling 24 h after injection of the eliciting virus. DTH mice sensitized with noninfectious virus was elicited only by virus that shared hemagglutinin specificity with the sensitizing virus, whereas footpad injection of a given A-strain virus (A/WSN) could elicit DTH in mice sensitized with a variety of infectious A-strain viruses, including some not sharing hemagglutinin or neuraminidase specificities. The effector T cells generated in mice sensitized with either form of virus were sensitive to anti-Ly 1.1 serum and complement, but not to anti-Ly 2.1 serum and complement. Adoptive transfer of DTH was H-2 restricted. With spleen cells from mice sensitized subcutaneously with either infectious or noninfectious virus, sharing of the IA region was both necessary and sufficient for successful transfer to occur. Cells recovered from infected mouse lungs, and secondary effector cells generated in vitro transferred DTH if injected into the footpad with the eliciting virus. The effector cells had the Ly 1 phenotype, and, in both cases, the cells were I restricted. These results contrast with earlier findings that transfer of DTH to lymphocytic choriomeningitis virus infection required K- or D-region sharing between donor and recipient. Thus, the earlier hypothesis that multiplying infectious agents such as viruses would "alter" K- or D-coded, rather than I-coded, structures is not generally correct.

The effect of specific antibody on the generation of cytotoxic T lymphocytes and the recovery of mice from influenza virus infection

A study has been made of the effect of humoral antibody on the generation of specific cytotoxic T cells (Tc) in the spleen or lungs after intravenous injection or intranasal inoculation of infectious influenza virus. Antibody injected before or at the same time as virus inhibited completely the generation of Tc in the spleen. If injected 1 h after virus, the inhibition was reduced by 50%, and little inhibition occurred if antibody was injected 6 h after virus. This suggested that antibody failed to influence Tc generation once infection of stimulating cells had occurred. Antibody injected intravenously 24 h after intranasal inoculation of virus into normal mice did not affect the level of cytotoxic activity present in the lungs, and trace amounts only (less than 1 log10 EID50) could be recovered from the lungs at 6 days. As there is a high titre (greater than 6 log10 EID50) of infectious virus in the lungs of mice 24 h after infection, this represents a very efficient control mechanism. The same protocol carried out with athymic mice gave only a partial clearance (c. 3 log10 EID50) of virus in the lungs. It was suggested that a major role of humoral antibody was to limit infection by the virus, and in this respect it complemented the action of Tc.