Comparative clonal analysis of human immunodeficiency virus type 1 (HIV-1)-specific CD4+ and CD8+ cytolytic T lymphocytes isolated from seronegative humans immunized with candidate HIV-1 vaccines.

The lysis of infected host cells by virus-specific cytolytic T lymphocytes (CTL) is an important factor in host resistance to viral infection. An optimal vaccine against human immunodeficiency virus type 1 (HIV-1) would elicit virus-specific CTL as well as neutralizing antibodies. The induction by a vaccine of HIV-1-specific CD8+ CTL in humans has not been previously reported. In this study, CTL responses were evaluated in HIV-1-seronegative human volunteers participating in a phase I acquired immune deficiency syndrome (AIDS) vaccine trial involving a novel vaccine regimen. Volunteers received an initial immunization with a live recombinant vaccinia virus vector carrying the HIV-1 env gene and a subsequent boost with purified env protein. An exceptionally strong env-specific CTL response was detected in one of two vaccine recipients, while modest but significant env-specific CTL activity was present in the second vaccinee. Cloning of the responding CTL gave both CD4+ and CD8+ env-specific CTL clones, permitting a detailed comparison of critical functional properties of these two types of CTL. In particular, the potential antiviral effects of these CTL were evaluated in an in vitro system involving HIV-1 infection of cultures of normal autologous CD4+ lymphoblasts. At extremely low effector-to-target ratios, vaccine-induced CD8+ CTL clones lysed productively infected cells present within these cultures. When tested for lytic activity against target cells expressing the HIV-1 env gene, CD8+ CTL were 3-10-fold more active on a per cell basis than CD4+ CTL. However, when tested against autologous CD4+ lymphoblasts acutely infected with HIV-1, CD4+ clones lysed a much higher fraction of the target cell population than did CD8+ CTL. CD4+ CTL were shown to recognize not only the infected cells within these acutely infected cultures but also noninfected CD4+ T cells that had passively taken up gp120 shed from infected cells and/or free virions. These results were confirmed in studies in which CD4+ lymphoblasts were exposed to recombinant gp120 and used as targets for gp120-specific CD4+ and CD8+ CTL clones. gp120-pulsed, noninfected targets were lysed in an antigen-specific fashion by CD4+ but not CD8+ CTL clones. Taken together, these observations demonstrate that in an in vitro HIV-1 infection, sufficient amounts of gp120 antigen are produced and shed by infected cells to enable uptake by cells that are not yet infected, resulting in the lysis of these noninfected cells by gp120-specific, CD4+ CTL.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of CD4+ human cytolytic T cells specific for HIV-infected cells by a gp160 subunit vaccine.

Cytolytic T lymphocyte (CTL) responses were evaluated in humans immunized with recombinant human immunodeficiency virus type 1 (HIV) envelope glycoprotein gp160. Some vaccinees had gp160-specific CTLs that were shown by cloning to be CD4+. Although induced by exogenous antigen, most gp160-specific CTL clones also recognized gp160 synthesized endogenously in target cells. These clones lysed autologous CD4+ T lymphoblasts infected with HIV. Of particular interest were certain vaccine-induced clones that lysed HIV-infected cells, recognized gp160 from diverse HIV isolates, and did not participate in "innocent bystander" killing of noninfected CD4+ T cells that had bound gp120.

Comparison of the immune response to recombinant gp120 in humans and chimpanzees.

OBJECTIVE: To assess similarities and differences in antibody responses to recombinant (r) HIV-1IIIB gp120 in chimpanzees, previously protected from HIV-1 infection, and human volunteers immunized in connection with a Phase I clinical trial. METHODS: Frozen sera from humans immunized with rgp120 from HIV-1IIIB and chimpanzees immunized with the same antigen or recombinant soluble gp160 were compared in a variety of serologic assays. RESULTS: The magnitude of the antibody response to gp120 was similar in both species; however, the half-life of the antibody response to rgp120 was approximately 4.5 times longer in humans (9 weeks) than in chimpanzees (2 weeks). Antibodies to gp120 in both species were broadly cross-reactive with gp120 from diverse isolates of HIV-1 and were effective in blocking the binding of gp120 to CD4. Antibody binding to native gp120 was greater than to denatured gp120 in both species. Antibody responses to the principal neutralizing determinant (V3 domain) and virus neutralization titers were approximately 10-fold lower in humans than chimpanzees. The relative avidity of antibody binding to gp120 was higher in the sera from the immunized chimpanzees than in the immunized humans. CONCLUSIONS: While the antibody responses to rgp120 elicited in man and chimpanzees were in many ways similar, significant differences did occur. Predictions made on the basis of chimpanzee immunogenicity studies over-estimated the potency of the virus neutralizing titers and under-estimated the duration of the antibody response achieved in humans.

Mechanical load opposes angiotensin-mediated decrease in vascular alpha 1-adrenoceptors.

alpha 1-Adrenergic receptor contraction of vascular smooth muscle is augmented by increases in angiotensin II and also in several forms of hypertension. Whether angiotensin directly modulates alpha 1-adrenoceptor subtype expression to contribute to this effect is unknown. In a previous study, we demonstrated that increased mechanical load (pressure) per se does not alter expression of alpha 1B- and alpha 1D-adrenoceptors in rat aortic smooth muscle in cell culture, in vitro or in vivo. However, findings in aortic coarctation hypertension suggested that a humoral factor, possibly angiotensin, selectively reduces alpha 1B-adrenoceptors and that increased mechanical load opposes this decrease. The present study examined this hypothesis by determining the effect of angiotensin alone and in the presence of mechanical loading on the expression of alpha 1D- and alpha 1B-adrenergic receptor mRNAs and alpha 1-receptor density in cultured aortic smooth muscle cells. alpha 1D mRNA content, per smooth muscle cell, concentration-dependently decreased after 3 hours of exposure to 0.3 nmol/L to 1 mumol/L angiotensin but by 24 hours had returned to control levels. In contrast, alpha 1B mRNA concentration-dependently declined at a later time (24 hours) and remained decreased at 48 hours to 27 +/- 6% of control with 1 mumol/L angiotensin. Angiotensin also decreased alpha 1-adrenoceptor density in a dose-dependent manner. Angiotensin had no effect on cell number in these confluent, quiescent cells but did increase cell protein and total RNA. This cellular hypertrophy and the decreases in alpha 1-adrenoceptor mRNAs were blocked by the angiotensin type 1 receptor antagonist losartan. Cyclic mechanical loading of smooth muscle cells opposed the angiotensin-mediated hypertrophy and decrease in alpha 1B mRNA expression and alpha 1-adrenergic receptor density. These data suggest that angiotensin and intravascular pressure interact to affect cell growth and expression of alpha 1B-adrenergic receptors by vascular smooth muscle.

Effect of mechanical loading on vascular alpha 1D- and alpha 1B-adrenergic receptor expression.

Heterogeneous distribution and function of alpha 1-adrenergic receptor subtypes on arterial and venous vessels, together with evidence for altered alpha-adrenergic receptor expression in hypertension, led us to examine whether mechanical load influences expression of alpha 1B- and alpha 1D-adrenergic receptors in rat aortic smooth muscle cells (SMCs). We used RNase protection and radioligand binding assays to measure mRNA and alpha 1-adrenergic receptor density. In the first model, SMCs were subjected to phasic loading using flexible culture plates. As a positive control for the load stimulus, postconfluent, quiescent passage 5 cells demonstrated the expected load-dependent morphological realignment. However, no changes were detected in expression of either alpha 1D- or alpha 1B-adrenergic receptor mRNAs or receptor density after 24 to 48 hours of loading. beta-Actin and SMC-specific alpha-actin mRNA, as well as cell number and per-cell total RNA and protein, were also unaffected. In a second model, intact thoracic aortas, in either the presence or absence of endothelial cells, were cultured for 48 hours under tonic load. Like cultured cells, 48 hours of load did not affect SMC expression of alpha 1-adrenergic receptor mRNAs. We used suprarenal aortic coarctation to examine effects of increased pressure in vivo. As with the previous in vitro and in situ models, hypertension (30 days) had no effect on expression of alpha 1B- and alpha 1D-adrenergic receptor mRNAs in the suprarenal aorta compared with sham coarctation. To separate pressure per se from humoral influences, we also measured mRNAs in the subrenal, normotensive aorta, alpha 1B mRNA levels decreased to 68 +/- 14% of sham-coarcted controls in subrenal aorta exposed to normal blood pressure but also to systemic humoral changes induced by coarctation. As a positive control for a load effect, SMC-specific alpha-actin mRNA increased for loaded aorta in organ culture and in hypertensive aorta in vivo, whereas expression of beta-actin mRNA was unaffected. These results from cell culture, organ culture, and in vivo models suggest that pressure (load) alone has no effect on alpha 1B- and alpha 1D-adrenergic receptor expression. In coarctation hypertension, smooth muscle protected from the hypertension showed a decline in alpha 1B mRNA that may be due to a humoral factor or factors.

Antibodies to recombinant gp160 in mucosal secretions and sera of persons infected with HIV-1 and seronegative vaccine recipients.

An enzyme immunoassay (EIA) was developed to detect secretory IgA (sIgA) antibodies to HIV-1 envelope glycoprotein, using a mouse monoclonal antibody and a highly purified, baculovirus-expressed recombinant gp160 (rgp160) as antigen. Detection of sIgA was enhanced by prior immunoprecipitation of IgG. IgG and sIgA rgp160 antibodies were measured in parotid saliva and nasal wash samples of 18 HIV-1-seropositive volunteers and 14 HIV-1-seronegative adult volunteers immunized 3 times with HIV-1 IIIB rgp160 vaccine at 1 of 4 dosage levels: 40 micrograms (N = 3), 80 micrograms (N = 3), 160 micrograms (N = 4), and 640 micrograms (N = 4). We detected rgp160-specific IgG antibody in the nasal wash samples of all HIV-1-seropositive volunteers and 4/8 vaccinees (50%) immunized with the two highest doses of rgp160 vaccine. All infected volunteers tested had rgp160-specific sIgA in their nasal wash samples. None of the vaccinees and very few of infected volunteer specimens had detectable antibody in the parotid saliva samples (5/8 had IgG and 1/8 had sIgA). We also detected IgG antibody to rgp160 in the sera of all infected volunteers and 13/14 vaccinees (93%). With this EIA, sIgA antibody can be measured in mucosal secretions of recipients of appropriate candidate HIV-1 vaccines.

Cytokines from vaccine-induced HIV-1 specific cytotoxic T lymphocytes: effects on viral replication.

Cytolytic T lymphocytes (CTLs) specific for the human immunodeficiency virus (HIV-1) envelope glycoproteins have been cloned from HIV-1-seronegative human volunteers immunized with HIV-1 gp160-based candidate vaccines. Although vaccine-induced CTLs can potentially contribute to the antiviral response by direct lysis of infected cells, these CTLs may also produce cytokines that alter HIV-1 gene expression in other infected cells present in the microenvironment where CTL-target cell interactions occur. Vaccine-induced CTL clones were therefore examined for production of cytokines that affect HIV-1 gene expression in chronically infected T lymphocytic and promonocytic cell lines. Enhancement of HIV-1 gene expression was observed with supernatants from CD4+ CTL clones and with supernatants from a subset of CD8+ CTL clones. For each clone studied, upregulation of HIV-1 gene expression in chronically infected T cell lines resulted from the antigen-specific release by CTLs of tumor necrosis factor alpha (TNF-alpha). CD4+ and CD8+ CTLs that released TNF-alpha on antigen stimulation were also shown to express a biologically active 26-kDa transmembrane form of TNF-alpha, which was sufficient to induce upregulation of HIV-1 gene expression in chronically infected T cells placed in direct contact with the CTLs. Supernatants from antigen-activated, vaccine-induced CD4+ and CD8+ CTLs also caused upregulation of HIV-1 gene expression in chronically infected promonocytic cells. A subset of CD8+ CTL clones also produced a soluble factor(s) that inhibited HIV-1 replication in acutely infected autologous CD4+ blasts. Supernatants from CD4+ CTLs had no effect on HIV-1 replication in acutely infected CD4+ blasts. These results suggest that cytokine production as well as cytolytic activity should be evaluated in the analysis of the potential antiviral effects of vaccine-induced CTLs.

Characterization of serum antibody responses to recombinant HIV-1 gp160 vaccine by enzyme immunoassay. NIAID AIDS Vaccine Clinical Trials Network.

An enzyme immunoassay (EIA) was developed to measure serum antibody responses of healthy adult volunteers vaccinated with 40 or 80 micrograms of human immunodeficiency virus type 1 (HIV-1) recombinant gp160 (rgp160) vaccine at 0, 1, 6, and 18 months. This assay, which used purified rgp160 as antigen, was compared with the Biotech/Du Pont HIV-1 Western blot and the Abbott HIV-1 EIA. Of 33 volunteers who received three doses of rgp160 vaccine, seroresponses were detected in 91% by rgp160 EIA, 97% by Western blot, and 30% by HIV-1 EIA. The level of IgG rgp160 EIA antibody (mainly IgG1) peaked after the third immunization; 64% of 33 vaccinees still had detectable antibody by 12 months. The fourth immunization induced anamnestic IgG EIA antibody in 23 of 24 vaccinees, with titers ranging from 1:200 to 1:25,600. Neutralizing antibody was not detected in postvaccination sera by microtiter syncytium formation inhibition assay. Additional testing of sera by EIA indicated that the immune response to the vaccine was directed toward epitopes on both gp120 and gp41. Seroresponses to the immunodominant epitopes on gp41 were infrequent and none were detected to the neutralization epitope in the V3 region of gp120. This highly sensitive EIA is useful for characterizing HIV-1-specific antibody responses induced by an HIV-1 gp160 subunit vaccine.

Studies of high doses of a human immunodeficiency virus type 1 recombinant glycoprotein 160 candidate vaccine in HIV type 1-seronegative humans. The AIDS Vaccine Clinical Trials Network.

We examined the safety and immunogenicity of a baculovirus-derived recombinant HIV-1 envelope glycoprotein vaccine candidate, rgp160 (VaxSyn; MicroGeneSys, Meriden, CT), administered at doses of 160 or 640 micrograms to 56 healthy, HIV-1-seronegative adults, in a randomized, double-blind, placebo-controlled study. Immunizations were given intramuscularly at 0, 1, 6, and 12 months. Both doses were generally well tolerated, although self-limited local reactions were frequent. No other clinical or laboratory toxicities were noted, and no effects on CD4 or CD8 lymphocyte counts or percentages were noted. Serum antibody responses to HIV proteins were detected by Western blot (WB) in 19 of 20 and in 19 of 19 recipients of four doses of 160 and 640 micrograms, respectively. Western blot responses developed more rapidly in the 640-micrograms group. High rates of EIA antibody responses to HIV-1 lysate were also present in both groups, and developed more rapidly in the 640-micrograms group. Enzyme immunoassay antibody responses to the immunogen (rgp160) were also frequent, but were infrequent to V3 to gp41 peptides. Neutralizing antibodies against the homologous HIV-1 LAI isolate were seen in 3 of 20 subjects (GMT = 11) who received four doses of 160 micrograms, and in 10 of 19 subjects who received four doses of 640 micrograms (GMT = 32). Fusion inhibiting antibody was not detected. CD4 blocking activity was seen in 3 of 19 subjects who received four doses of 640 micrograms. Complement-mediated antibody-dependent enhancement was found in sera from 11 of 19 volunteers in the 640-micrograms group. Lymphocyte proliferative responses to the immunogen were detected in 4 of 4 subjects tested, but no cytotoxic T cell activity was noted in 11 subjects. Administration of the 640-micrograms dose of this rgp160 vaccine candidate relative to the lower doses was associated with increased immunogenicity, including higher rates of homologous neutralizing antibody responses, although at low titer.

Evaluation of a live attenuated bovine parainfluenza type 3 vaccine in two- to six-month-old infants.

BACKGROUND: A safe and effective parainfluenza type 3 (PIV-3) virus vaccine is needed to prevent serious PIV-3-associated illness in infants younger than 6 months of age. In previous studies a live bovine PIV-3 (BPIV-3) vaccine, which was developed to prevent human PIV-3 (HPIV-3) disease, was shown to be safe, infectious, immunogenic and phenotypically stable in 6- to 36-month-old infants and children. METHODS: The safety, infectivity and immunogenicity of a single dose of the BPIV-3 vaccine was evaluated in a randomized, placebo-controlled, double blinded trial in 19 infants 2 to 5.9 months of age and in 11 additional 6- to 36-month-old subjects. RESULTS: The BPIV-3 vaccine was well-tolerated in both age groups and infected 92% of those younger than 6 months and 89% of those older than 6 months of age. Serum hemagglutination-inhibition (HAI) antibody responses to HPIV-3 and to BPIV-3, respectively, were detected in 42 and 67% of the younger infants, compared with 70 and 85% of the older subjects. In the younger infants we analyzed the rate of antibody response by titer of maternally acquired antibodies; low titer was defined as a preimmunization serum HAI titer < 1:8 and high titer was defined as a preimmunization serum HAI titer > or = 1:8. Young infants with a low titer of maternally acquired antibodies were significantly more likely to respond to the BPIV-3 vaccine that those with a high titer (89% vs. none for serum HAI response to BPIV-3; P = 0.02, Fisher's exact test). CONCLUSIONS: This study demonstrated that the BPIV-3 vaccine was safe and infectious in infants younger than 6 months of age and was also immunogenic in the majority of these young infants. Additional studies are needed to determine whether two or more doses will enhance the immunogenicity of the BPIV-3 vaccine in young infants and to assess its safety and immunogenicity when given simultaneously with routine childhood immunizations.

Safety and immunogenicity of a cold-adapted influenza A (H1N1) reassortant virus vaccine administered to infants less than six months of age.

A safe and effective influenza vaccine is needed to prevent serious influenza illness in infants younger than 6 months of age. The purpose of this study was to determine whether two doses of the cold-adapted (ca) influenza A reassortant vaccine would be safe and immunogenic in this age group. In the first part of this study, infants received two doses of 10(5) or 10(6) 50% tissue culture-infectious dose (TCID50) of the ca influenza vaccine separately from routine immunizations. In the second part of this study two 10(6) TCID50 doses of the ca influenza vaccine were given with routine immunizations at 2 and 4 or 2 and 6 months of age. The ca influenza vaccine was well-tolerated by participants in both parts of this study. Two doses of the ca influenza vaccine were immunogenic in infants who received them separately from routine immunizations; 83% of vaccinees developed protective titers of serum hemagglutination-inhibition (HAI) antibody. In contrast, when the ca vaccine was administered with routine immunizations, protective HAI antibody titers were induced in only 20% of those immunized at 2 and 4 months of age and 50% of those immunized at 2 and 6 months of age. There were no statistically significant associations between HAI antibody response to ca influenza vaccination and dose schedule, presence of passively acquired maternal HAI antibody, ethnic group or breast-feeding status. Young age at the time of first immunization, however, appeared to correlate with decreased response to the hemagglutinin antigen of the influenza A virus.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced infectivity of cold-adapted influenza A H1N1 viruses in the elderly: correlation with serum and local antibodies.

OBJECTIVE: To compare young and elderly adults in terms of their immune responses and rates of infection following intranasal vaccination with a live attenuated influenza virus. DESIGN: Time series, comparing outcomes in young and elderly convenience sample. METHOD: Retrospective laboratory analysis of serum and nasal wash specimens collected during prior studies in which young or elderly volunteers had been inoculated with cold-adapted influenza A/Kawasaki/86 (H1N1) reassortant virus. SETTING: Johns Hopkins Center for Immunization Research. PARTICIPANTS: Healthy young and elderly adults with pre-vaccination serum hemagglutination inhibition (HAI) antibody titers less than or equal to 1:8. OUTCOME MEASUREMENTS: Antibody responses in serum and nasal washes. MAIN RESULTS: The proportion of vaccinees who developed any serum or local antibody response was higher in young compared with elderly subjects (20/20 vs 5/14, P less than 0.0005). Resistance to infection with cold-adapted virus correlated with pre-vaccination levels of serum immunoglobulin G (IgG), serum IgA, and nasal wash IgA antibody to whole virus antigen. Age was highly correlated with a lack of response to vaccine by simple regression, but not when data were adjusted for pre-existing antibody levels. CONCLUSIONS: Cold-adapted reassortant influenza A H1N1 viruses achieve lower rates of infection in elderly than young adults, primarily due to age-related differences in preexisting levels of immunity which may not be reflected by HAI titer.

Hepatitis B virus vaccination for older adults.

OBJECTIVE: To compare in adults more than 50 years old the tolerability and immunogenicity of vaccination with recombinant hepatitis B surface antigen (HBs) compared with vaccination with recombinant hepatitis B protein PreS2 + S, and to investigate the safety and immunogenicity of a fourth vaccine dose in poor and non-responders. DESIGN: Randomized, double-blind prospective study. SETTING: General clinical research center for outpatient evaluation and vaccination. SUBJECTS: Adults older than age 50 who were in general good health and with no known risk factors for acquiring or serologic evidence of hepatitis B virus infection. INTERVENTION: Subjects were randomized to receive 10 mcg HBs (Recombivax, Merck, Sharp and Dohme), 12 mcg PreS2 + S, or 24 mcg PreS2 + S vaccine at 0, 1, and 6 months. Poor and non-responders (anti-Hbs < 10 mIU/mL at month 9 and/or 12) were encouraged to receive a fourth vaccine injection. MEASUREMENTS: Diary records of temperature and local and systemic reactions following each vaccination were maintained by all subjects. Anti-HBs levels were measured by radioimmunoassay before the first injection, at 1, 2, 3, 6, 7, 9, and 12 months after for all subjects, and 1 month after the fourth injection for the group of poor and non-responders. MAIN RESULTS: Twenty men and nine women (mean age +/- SD, 66 +/- 8.0 years) were enrolled. Ten subjects received HBs vaccine, nine received 12 mcg PreS2 + S vaccine, and 10 received 24 mcg PreS2 + S vaccine. One subject in the HBs group dropped out, and data were analyzed for the remaining 28 subjects. There were no differences in rates of side effects reported by each of the three groups. Overall, minor local adverse reactions occurred in 12 (40%) after at least one of the first three vaccinations. Systemic side effects occurred in five (17%) after the first vaccination, in one after the second, but in none after the third. The 24-mcg PreS2 + S vaccine was not more immunogenic than the HBs vaccine, and the 12-mcg PreS2 + S vaccine was judged inadequate. Nineteen of 22 (86%) poor and non-responders received a fourth vaccination. Minor local adverse reactions were reported by six (32%), and none reported a systemic side effect. For the 12 subjects receiving a fourth injection of HBs or 24 mcg PreS2 + S vaccine, the proportion of responders 1 month following the fourth injection was greater than for 1 month following the third injection (11 of 12 [92%] versus 12 of 19 [63%], respectively, P < .05). CONCLUSION: For adults more than 50 years of age who have low anti-HBs levels after three vaccine injections, a fourth injection is well tolerated and results in improved immunogenic response.

Cell-mediated immune responses of adults to vaccination, challenge with Rickettsia rickettsii, or both.

As a part of a study to evaluate a formalin-killed Rickettsia rickettsii vaccine, lymphoproliferative (LT) and delayed-type hypersensitivity (DTH) skin test responses to killed R. rickettsii were measured as correlates of cell-mediated immunity in volunteers who were vaccinated, challenged with R. rickettsii, or both. We detected LT responses in 26 (51%) of 51 volunteers after vaccination. After challenge, six of six unvaccinated volunteers and 12 of 16 vaccinated volunteers developed Rocky Mountain spotted fever (RMSF); all 22 mounted LT responses. The vaccinated individuals developed LT responses of greater magnitude and 1-2 weeks earlier than unimmunized controls (41,049 versus 15,084 mean net counts per minute [cpm]), suggesting that vaccination primed the cellular immune system. Moreover, development of LT responses postvaccination was associated with the amelioration of RMSF, as indicated by a slightly longer mean incubation period (328 hr versus 302 hr) and a shorter illness (19 hr versus 26 hr) in LT responders than in LT nonresponders. However, the postvaccination LT response did not discriminate between vaccinated individuals who resisted challenge and those who did not. Skin tests using killed R. rickettsii as antigen, performed in volunteers 14-17 months postvaccination or 12-15 months after challenge, revealed a weak but significant reaction in 50% of those who had received vaccine only, and a moderately strong reaction in all vaccinated and unvaccinated volunteers who had been challenged with R. rickettsii. The relationships between induction of protective immunity against intracellular bacteria by killed and replicating organisms and LT and DTH responses are discussed.

Association between O blood group and occurrence and severity of diarrhoea due to Escherichia coli.

During studies of diarrhoea due to Escherichia coli in 316 adult volunteers, ABO and Rh blood group determinations were done to look for differences in the occurrence or severity of illness in association with certain blood groups. In studies using heat-labile enterotoxin-producing E. coli, volunteers with O blood group had a significantly higher attack rate for diarrhoea than persons with other blood groups. In contrast, in studies with enteropathogenic or heat-stable enterotoxin-producing E. coli, no association was found between occurrence of diarrhoea and ABO group. These studies, and previous studies finding a similarly increased susceptibility to cholera in persons with O blood group, suggest that the mechanism of increased risk involves an interaction between blood group substances and the similar enterotoxin produced by E. coli and Vibrio cholerae.

Susceptibility to virus infection with exposure to nitrogen dioxide.

The interaction between nitrogen dioxide (NO2) exposure and human susceptibility to respiratory virus infection was investigated in a placebo-controlled, randomized, blinded trial that was conducted in an environmentally controlled research chamber over a three-year period. Healthy, non-smoking volunteers, 18 to 35 years old, who were seronegative to influenza A/Korea/82 (H3N2) virus, were randomly assigned either to breathe filtered clean air (clean air group) or nitrogen dioxide (exposure group) for two hours a day for three consecutive days. The nitrogen dioxide concentrations were 2 ppm (Year 1), 3 ppm (Year 2), and 1 or 2 ppm (Year 3). Live, attenuated cold-adapted (ca) influenza A/Korea/82 reassortant virus was administered intranasally to all subjects after the second day of exposure. Only one of the 152 volunteers had any symptoms, and that subject had only a low-grade fever. No adverse changes in pulmonary function or nonspecific airway reactivity to methacholine were observed after 2 or 3 ppm nitrogen dioxide exposure, virus infection, or both. Infection was defined by virus recovery, a four-fold or greater increase in serum or nasal wash influenza-specific antibody titers, or both. The infection rates of the groups exposed to nitrogen dioxide and those breathing clean air were: 12/21 (2 ppm nitrogen dioxide) versus 15/23 (clean air) in Year 1; 17/22 (3 ppm nitrogen dioxide) versus 15/21 (clean air) in Year 2; and 20/22 (2 ppm nitrogen dioxide) and 20/22 (1 ppm nitrogen dioxide) versus 15/21 (clean air) in Year 3. Although the differences were not statistically significant, the groups exposed to 1 or 2 ppm nitrogen dioxide in the last year became infected more often (91 percent) than those breathing clean air (71 percent). The frequencies of infection in two of the four groups exposed to nitrogen dioxide were higher than the 56 to 73 percent infection rate observed in previous studies in healthy human volunteers with the same dose of ca-influenza A (H3N2) virus. Our findings suggest, but do not prove, that nitrogen dioxide alone may play a role in increasing the susceptibility of adults to respiratory virus infections.