Proceedings of a workshop to discuss the epidemiology of invasive Haemophilus influenzae disease with emphasis on serotype a and b in the Americas, 2019

On March 9, 2019, a one-day workshop titled "The current epidemiology of invasive Haemophilus influenzae disease in the Americas", jointly organized by the Public Health Agency of Canada (PHAC), the Canadian Institute of Health Research (CIHR), and the National Research Council Canada (NRC), brought together experts in the epidemiology and surveillance of invasive Haemophilus influenzae (Hi) disease from the Pan American Health Organization (PAHO) and its five regional reference laboratories in South America, USA, and Canada in Ottawa, Ontario, Canada. This workshop built upon recommendations of previous related workshops and incorporated updated data.

Tuberculosis in the Circumpolar Region, 2006-2012

SETTING

The northern circumpolar jurisdictions Canada (Northwest Territories, Nunavik, Nunavut, Yukon), Finland, Greenland, Norway, Russian Federation (Arkhangelsk), Sweden and the United States (Alaska).

OBJECTIVE

To describe and compare demographic, clinical and laboratory characteristics, including drug resistance and treatment completion, of tuberculosis (TB) cases in the northern circumpolar populations.

DESIGN

Descriptive analysis of all active TB cases reported from 2006 to 2012 for incidence rate (IR), age and sex distribution, sputum smear and diagnostic site characteristics, drug resistance and treatment completion rates.

RESULTS

The annual IR of TB disease ranged from a low of 4.3 per 100 000 population in Northern Sweden to a high of 199.5/100 000 in Nunavik, QC, Canada. For all jurisdictions, IR was higher for males than for females. Yukon had the highest proportion of new cases compared with retreatment cases (96.6%). Alaska reported the highest percentage of laboratory-confirmed cases (87.4%). Smear-positive pulmonary cases ranged from 25.8% to 65.2%. Multidrug-resistant cases ranged from 0% (Northern Canada) to 46.3% (Arkhangelsk). Treatment outcome data, available up to 2011, demonstrated >80% treatment completion for four of the 10 jurisdictions.

CONCLUSION

TB remains a serious public health issue in the circumpolar regions. Surveillance data contribute toward a better understanding and improved control of TB in the north.

Prevalence of Helicobacter pylori among Alaskans: Factors associated with infection and comparison of urea breath test and anti-Helicobacter pylori IgG antibodies

BACKGROUND

Helicobacter pylori is one of the most common human infections in the world, and studies in Alaska Native people, as well as other Indigenous peoples, have shown a high prevalence of this gastric infection. This study was undertaken to determine the prevalence of H. pylori infection by urea breath test (UBT) and anti- H. pylori IgG among Alaskans living in four regions of the state and to identify factors associated with infection.

METHODS

A convenience sample of persons > 6 months old living in five rural and one urban Alaskan community were recruited from 1996 to 1997. Participants were asked about factors possibly associated with infection. Sera were collected and tested for anti- H. pylori IgG antibodies; a UBT was administered to participants > 5 years old.

RESULTS

We recruited 710 people of whom 571 (80%) were Alaska Native and 467 (66%) were from rural communities. Rural residents were more likely to be Alaska Native compared with urban residents (P < .001). Of the 710 people, 699 (98%) had a serum sample analyzed, and 634 (97%) persons > 5 years old had a UBT performed. H. pylori prevalence was 69% by UBT and 68% by anti- H. pylori IgG. Among those with a result for both tests, there was 94% concordance. Factors associated with H. pylori positivity were Alaska Native racial status, age ≥ 20 years, rural region of residence, living in a crowded home, and drinking water that was not piped or delivered.

CONCLUSIONS

Helicobacter pylori prevalence is high in Alaska, especially in Alaska Native persons and rural residents. Concordance between UBT and serology was also high in this group. Two socioeconomic factors, crowding and drinking water that was not piped or delivered, were found to be associated with H. pylori positivity.

Persistence of antibody to Hepatitis A virus 20 years after receipt of Hepatitis A vaccine in Alaska

Hepatitis A vaccine is recommended for children ≥1 year old to prevent hepatitis A virus (HAV) infection. However, the duration of vaccine-induced immunity is unknown. We evaluated a cohort of Alaska Native persons 20 years after HAV vaccination. Children aged 3-6 years had been previously randomized to receive three doses of HAV vaccine (360 ELISA units/dose) at: (i) 0,1,2 months; (ii) 0,1,6 months; and (iii) 0,1,12 months. We measured anti-HAV antibody concentrations every 2-3 years; described geometric mean concentrations (GMC) and the proportion with protective antibody (≥20 mIU mL^-1 ) over time; and modelled the change in GMC using fractional polynomial regression. Of the 144 participants, after 20 years 52 (36.1%) were available for the follow-up (17, 18, 17 children in Groups A, B and C, respectively). Overall, 46 (88.5%) of 52 available participants had anti-HAV antibody concentrations ≥20 mIU mL^-1 , and overall GMC was 107 mIU mL^-1 . Although GMC levels were lower in Group A (60; CI 34-104) than in Group B (110; CI 68-177) or Group C (184; CI 98-345) (B vs C: P=.168; A vs B/C: P=.011), there was no difference between groups after adjusting for peak antibody levels post-vaccination (P=.579). Models predicted geometric mean concentrations of 124 mIU mL^-1 after 25 years, and 106 mIU mL^-1 after 30 years. HAV vaccine provides protective antibody levels 20 years after childhood vaccination. Lower antibody levels in Group A may be explained by a lower initial peak response. Our results suggest a booster vaccine dose is unnecessary for at least 25-30 years.

The emerging Haemophilus influenzae serotype a infection and a potential vaccine: Implementation science in action

Haemophilus influenzae serotype b (Hib) was a major cause of meningitis in children until Hib conjugate vaccine was introduced into the routine infant immunization program and Hib disease in children was almost eliminated. In Alaska, northern Canada and other countries with Indigenous peoples, H. influenzae serotype a (Hia) has emerged as a significant cause of pneumonia, meningitis and septic arthritis especially in children under 24 months of age. A joint government initiative between the Public Health Agency of Canada (PHAC) and the National Research Council of Canada (NRC) was carried out to assess whether an Hia vaccine could be developed for the common good. The initiative included strategic partnerships with clinician researchers in Thunder Bay, Ontario who provide health services to Indigenous people and the Artic Investigations Program (AIP) of the United States Centers for Disease Control and Prevention (CDC) in Alaska. This government initiated and funded research identified that the development of an Hia vaccine is possible and ongoing surveillance that includes strain characterization is essential to understand the potential spread of Hia in North America and around the world.

Molecular epidemiology of serotype 19A Streptococcus pneumoniae among invasive isolates from Alaska, 1986-2010

Background

After the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in Alaska, the incidence of invasive pneumococcal disease (IPD) due to non-vaccine serotypes, particularly serotype 19A, increased. The aim of this study was to describe the molecular epidemiology of IPD due to serotype 19A in Alaska.

Methods

IPD data were collected from 1986 to 2010 through population-based laboratory surveillance. Isolates were serotyped by the Quellung reaction and MICs determined by broth microdilution. Genotypes were assessed by multilocus sequence typing.

Results

Among 3,294 cases of laboratory-confirmed IPD, 2,926 (89%) isolates were available for serotyping, of which 233 (8%) were serotype 19A. Across all ages, the proportion of IPD caused by serotype 19A increased from 3.5% (63/1823) pre-PCV7 (1986–2000) to 15.4% (170/1103) post-PCV7 (2001–2010) (p<0.001); among children <5 years of age, the proportion increased from 5.0% (39/776) to 33.0% (76/230) (p<0.001). The annual incidence rate of IPD due to serotype 19A (all ages) increased from 0.73 cases pre-PCV7 to 2.56 cases/100,000 persons post-PCV7 (p<0.001); rates among children <5 years of age increased from 4.84 cases to 14.1 cases/100,000 persons (p<0.001). Among all IPD isolates with reduced susceptibility to penicillin, 17.8% (32/180) were serotype 19A pre-PCV7 and 64% (121/189) were serotype 19A post-PCV7 (p<0.001). Eighteen different sequence types (STs) were identified; ST199 or single locus variants of ST199 (n=150) and ST172 (n=59) accounted for the majority of isolates. Multidrug-resistant isolates were clustered in ST199 and ST320.

Conclusion

While PCV13 should significantly reduce the burden of disease due to 19A, these data highlight the need to continue surveillance for IPD to monitor the effects of vaccination on the expansion and emergence of non-PCV strains.

Clinical significance of elevated alpha-fetoprotein in Alaskan Native patients with chronic hepatitis C

The clinical significance of elevated serum alpha-fetoprotein (AFP) in patients with chronic hepatitis C virus (HCV) infection is not well defined. We analysed data from a population-based cohort of patients with HCV infection to assess the prevalence of elevated serum AFP, to determine its association with clinical and virologic parameters and with clinical outcomes. We defined a slightly elevated serum AFP level as 8 to <15 and a high-AFP level as > or =15 microg/L. Among 541 HCV-RNA-positive persons, 61 (11%) had a slightly elevated or high AFP at the time of consent. AFP > or =8 microg/L was associated with the older age, aspartate aminotransferase/alanine aminotransferase ratio >1, and higher alkaline phosphatase levels, but not with heavy alcohol use, IV drug use, genotype, viral load or duration of HCV infection. Among 192 persons with an AFP at liver biopsy, 17% had an AFP > or =8 microg/L. The sensitivity/specificity of an AFP level > or =8 in detecting Ishak 3-6 fibrosis was 39%/95%. Among 372 persons with a minimum of four AFP measurements over 6 years, 5% had persistently elevated AFP >8 microg/L, 19% had both elevated and normal AFP measurements, and 76% had persistently normal AFP. Elevated AFP at consent was associated with hepatocellular carcinoma (HCC) and end-stage liver disease. Over 6 years of follow-up, persistently elevated AFP was associated with the development of HCC; no person with AFP persistently <8 microg/mL developed HCC. Serial AFP measurements appear to be useful in identifying persons with advanced fibrosis and help to determine who needs periodic screening with liver ultrasound to detect HCC.

Reinfection after successful eradication of Helicobacter pylori: a 2-year prospective study in Alaska Natives

BACKGROUND

Limited information exists regarding risk factors for reinfection after cure of Helicobacter pylori infection.

AIM

To determine the 2-year reinfection rate of H. pylori in a cohort of urban Alaska Natives.

METHODS

Participants over 18 years of age undergoing oesophagogastroduodenoscopy had (13)C urea breath test, culture, CLOtest and histology performed. Those diagnosed with H. pylori who tested urea breath test-negative at 8 weeks after treatment were followed prospectively at 4 months, 6 months, 1 year and 2 years. Subjects experiencing H. pylori reinfection as defined by a positive urea breath test were compared with those who did not become reinfected using univariable and multivariable analysis. Risk of reinfection over time was estimated by the Kaplan-Meier method.

RESULTS

Helicobacter pylori reinfection occurred in 14 of 98 subjects successfully treated. The cumulative reinfection rate was 5.1% (95% CI: 0.7%-9.5%) at 4 months, 7.2% (2.0-12.3%) at 6 months, 10.3% (4.2-16.3%) at 1-year and 14.5% (7.5-21.6%) at 2 years. In multivariable analysis, a history of previous peptic ulcer disease or presence of ulcer at time of study oesophagogastroduodenoscopy were the only risk factors associated with reinfection (P = 0.01).

CONCLUSIONS

Based on the findings from our study, subjects with a history of or current peptic ulcer disease should be followed, after successful treatment for H. pylori, with periodic urea breath test to detect reinfection, as reinfection would put them at high risk for ulcer recurrence.

Risk factors for meningococcal disease in college students

CONTEXT

Elevated rates of meningococcal disease were noted among 18- to 22-year-olds in the mid-1990s. However, national data on rates of meningococcal disease in US college students were not collected until 1998.

OBJECTIVES

To determine rates of meningococcal disease in US college students and to identify risk factors for meningococcal disease in this population.

DESIGN, SETTING, AND PATIENTS

Prospective surveillance study with nested case-control study of US college students with meningococcal infection from September 1, 1998, to August 31, 1999. Fifty state health departments and 231 college health centers participated.

MAIN OUTCOME MEASURES

Incidence of and risk factors for meningococcal disease in US college students.

RESULTS

Ninety-six cases of meningococcal disease were identified. The incidence rate for undergraduates was 0.7 per 100 000 persons vs 1.4 per 100 000 for the general population of 18- to 23-year-old nonstudents (P<.001). Freshmen living in dormitories had the highest incidence rate at 5.1 per 100 000. Of the 79 case-patients for whom information was available, 54 (68%) had illness due to vaccine-preventable meningococcal serogroups. On multivariable analysis of case-control study data, freshmen who lived in dormitories had an elevated risk of meningococcal disease (matched odds ratio, 3.6; 95% confidence interval, 1.6-8.5; P =.003) compared with other college students.

CONCLUSIONS

Freshmen who live in dormitories have an independent, elevated risk of meningococcal disease compared with other college students. Use of the currently available quadrivalent polysaccharide vaccine among college students could substantially decrease their risk of meningococcal disease.

Effect of oral rotavirus/iscom vaccines on immune responses in gnotobiotic lambs

A comparison of the effect on the immune responses in gnotobiotic lambs was made between an iscom vaccine prepared from recombinant rotavirus VP6 protein, an inactivated rotavirus/iscom-matrix vaccine and a vaccine comprising inactivated rotavirus alone. All three vaccines induced immunological priming and some degree of protection was observed after a single oral dose. However, different immune responses were induced in response to a virulent infection. The group vaccinated with the rotavirus/iscom-matrix vaccine showed a Th2-like response characterised by rotavirus-specific antibodies and a down-regulation of IFNgamma in jejunal Peyer's patches. Both Th1-like and Th2-like immune responses were induced in the group receiving the VP6 vaccine as seen by significantly increased expressions of IFNgamma and IL-6 in the jejunal Peyer's patch together with an increased percentage of CD8+ T cells in the intestine and rotavirus-specific antibodies at mucosal surfaces. Iscom vaccines given orally have the ability to induce both Th1-like and Th2-like immune responses in a ruminant model.

Characterisation of the primary local and systemic immune response in gnotobiotic lambs against rotavirus infection

This study characterised the primary immune response in gnotobiotic lambs after infection with a lamb rotavirus (RV). Lambs were infected and killed over a 7 week period together with controls. RV-ELISA and neutralising antibodies were determined in serum, nasal secretions, and intestinal scrapings. RV-antibody secreting cells (ASC) were enumerated in blood. Lymphocyte proliferations were determined in blood and gut-associated lymphoid tissues and cytokine expression was analysed in jejunal Peyer's patches (JPPs) and mesenteric lymph nodes (MLNs). Infected lambs cleared the virus by 8-9 days after infection without showing any clinical signs. The first indication of a specific immune response to RV was an increased expression of IL-4 mRNA in the JPPs in the infected group compared to the control group 3 days after infection. Rotavirus-specific IgA ASC in blood and IgA antibodies in serum and nasal secretions were detected from 7 days after infection followed at 10 days after infection by RV-specific IgG ASC and antibodies. Rotavirus-specific IgA antibodies were not detected in intestinal scrapings in the first 10 days after infection, but were detected by 52 days after infection. No RV-specific neutralising antibodies were seen in the intestine during the course of the experiment.

Intestinal cellular immunity after primary rotavirus infection

Infection of neonatal gnotobiotic lambs with a bovine strain of rotavirus was used to characterize the kinetics of the primary cellular intestinal immune response to this agent. At 2-3 days after infection virus was first detected in the faeces and increased numbers of CD45R+ cells were observed in peripheral blood. These cells persisted in significantly increased numbers in the circulation until 7-8 days after infection. At this time, virus was no longer detectable in the faeces. The increase in CD45R+ cells preceded the appearance of virus-neutralizing antibodies in the serum at 1 week after infection. Maximal antibody titres were reached 2 weeks after infection. Virus-primed cells were first observed 1 week after infection in the jejunal and ileal Peyer's patches, mesenteric lymph nodes and peripheral blood, and persisted in the mesenteric lymph nodes and jejunal Peyer's patches for a further 4 weeks. Analysis of lymphocyte surface antigens indicated that different sub-populations of lymphocytes were responding in the various lymphoid tissues; a majority of CD4+ cells was observed in the mesenteric lymph nodes, whereas B cells predominated in the ileal Peyer's patches.

Recognition of rotavirus antigens by mouse L3T4-positive T helper cells

A lymphocyte proliferation assay was used to examine the helper T cell response to rotavirus in mice following parenteral immunization with the UK strain of bovine rotavirus. Mixed populations of lymphocytes prepared from spleen or peripheral lymph nodes were tested for proliferation in the presence of UK strain rotaviruses, prepared as cell culture lysates, ultracentrifuged (pelleted) lysates, sucrose-purified virus and caesium chloride-purified virus. Live rotavirus induced non-specific stimulation of lymphocytes, which was not observed in response to inactivated virus. Putative helper T cells of the L3T4+ phenotype were prepared as an enriched population from UK strain-immunized mice or grown in vitro as a polyclonal T cell line. The response of L3T4(+)-enriched cells from mice immunized with inactivated virus was dependent on antigen-presenting cells (APCs). Cells obtained following immunization with live virus did not require further addition of APCs. The response of the L3T4+ T cell line was wholly dependent on APCs. UK strain-specific L3T4+ cells responded to whole UK rotavirus and to isolated VP6 of both UK and C486 rotavirus strains. The results indicate that virus-specific L3T4+ T cells are induced following rotavirus immunization and can respond to epitopes on VP6. UK strain-primed L3T4+ cells also responded to an avian rotavirus strain, Ch2, which shares only minimal serological cross-reactivity with the UK strain. T cell recognition of rotavirus may thus be broadly cross-reactive.

Regulation of mucosal responses by CD4+ T lymphocytes: effects of anti-L3T4 treatment on the gastrointestinal immune system

The role of CD4+ T cells in the gastrointestinal (GI) immune system in vivo was studied in mice selectively depleted of this subset by treatment with monoclonal anti-L3T4 (GK1.5) mAb. Treatment of young BALB/c mice with weekly injections of anti-L3T4 mAb resulted in a selective depletion of CD4+ T cells in both IgA effector (lamina propria regions of the intestine; LP) and inductive (Peyer's patch; PP) sites. However, levels of CD3+CD4-CD8+ and CD4-CD8- (double negative) T cells remained constant or increased. When sections of small intestine were assessed for the isotype of Ig-containing cells, normal mice contained predominantly IgA plasma cells with small numbers of IgM and IgG plasma cells while anti-L3T4 treatment dramatically reduced the numbers of IgA plasma cells. When numbers of IgA-producing cells were assessed by the isotype-specific ELISPOT assay, the LPL of anti-L3T4 mAb-treated mice showed an 80% reduction in the number of IgA spot-forming cells. The effect of anti-L3T4 mAb treatment on IgA inductive sites was also studied and this treatment reduced the overall size of PP as well as the germinal centers in this tissue. Although anti-L3T4 treatment depleted CD3+CD4+ T cells in PP, the relative frequency of surface IgA-positive (slgA+) B cells in this tissue did not change. These results show that repeated injection of anti-L3T4 mAb results in a CD4+ T cell deficiency in both IgA inductive (PP) and effector (LP) sites. The depletion of CD4+ T cells resulted in reductions in the numbers of mature IgA plasma cells present in the LP of gut-associated tissues, and reduced the overall size of PP including germinal centers, but did not affect the frequency of sIgA+ B cells in this IgA inductive site.

Regulatory function for murine intraepithelial lymphocytes. Two subsets of CD3+, T cell receptor-1+ intraepithelial lymphocyte T cells abrogate oral tolerance

The murine intraepithelial lymphocyte (IEL) population is enriched in T cells that express the gamma delta-TCR, however, the biologic function served by these T cells remains obscure. IEL are considered to be major effector cells in mucosal immunity, and we have investigated whether IEL subsets could reverse orally induced systemic unresponsiveness (oral tolerance; OT) and support secondary type responses when adoptively transferred to mice orally tolerized with SRBC. When purified CD3+ IEL from mice orally primed with SRBC were transferred to adoptive hosts and challenged with SRBC, splenic IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses were observed. However, CD3+ IEL from HRBC orally primed mice did not abrogate SRBC induced OT. Further, HRBC-primed CD3+, IEL converted HRBC-specific OT but not SRBC-specific OT. CD3+ IEL could be separated into four subsets based on expression of CD4 and CD8. CD3+, CD4-, 8+ T cells were the major subset (74.5%), with smaller numbers of CD4- and CD8- (double negatives, DN) (7.8%), CD4+, 8- (7.6%) and CD4+, CD8+ (double positives) (10.1%) T cells. Interestingly, both the CD3+, CD8+, and the CD3+, DN IEL subsets abrogated OT, resulting in significant IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses when adoptively transferred to mice with OT. However, neither CD3+, CD4+, CD8-, nor double positive T cells affected OT when studied in this system. The CD3+, CD8+ IEL subset could be further separated into Thy-1+ (16.6%) and Thy-1- (83.4%) cells; adoptive transfer of Thy-1- cells abrogated oral tolerance whereas the Thy-1+ subset was without effect. When the expression of TCR on IEL with this biologic function was determined by use of monoclonal anti-alpha beta TCR (H57.597), TCR2-, CD3+ IEL possessed immunoregulatory function whereas the alpha beta-TCR+ (TCR2+) fraction did not abrogate OT. Immunoprecipitation of membrane fractions obtained from purified CD3+, CD4-, CD8+, Thy-1- IEL with polyclonal anti-delta peptide (Tyr-Ala-Asn-Ser-Phe-Asn-Asn-Glu-Lys-Leu) antibody revealed bands of 45 and 35 kDa, corresponding to the delta- and gamma-chains, respectively. These results suggest that gamma delta-TCR+ IEL possess a regulatory function, namely the restoration of immune responses in a state of oral tolerance. Further, both CD3+, CD4-, CD8+, Thy-1-, and CD3+, DN IEL T cells exhibit this effector contrasuppressor function.

Regulatory function for murine intraepithelial lymphocytes. Two subsets of CD3+, T cell receptor-1+ intraepithelial lymphocyte T cells abrogate oral tolerance

The murine intraepithelial lymphocyte (IEL) population is enriched in T cells that express the gamma delta-TCR, however, the biologic function served by these T cells remains obscure. IEL are considered to be major effector cells in mucosal immunity, and we have investigated whether IEL subsets could reverse orally induced systemic unresponsiveness (oral tolerance; OT) and support secondary type responses when adoptively transferred to mice orally tolerized with SRBC. When purified CD3+ IEL from mice orally primed with SRBC were transferred to adoptive hosts and challenged with SRBC, splenic IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses were observed. However, CD3+ IEL from HRBC orally primed mice did not abrogate SRBC induced OT. Further, HRBC-primed CD3+, IEL converted HRBC-specific OT but not SRBC-specific OT. CD3+ IEL could be separated into four subsets based on expression of CD4 and CD8. CD3+, CD4-, 8+ T cells were the major subset (74.5%), with smaller numbers of CD4- and CD8- (double negatives, DN) (7.8%), CD4+, 8- (7.6%) and CD4+, CD8+ (double positives) (10.1%) T cells. Interestingly, both the CD3+, CD8+, and the CD3+, DN IEL subsets abrogated OT, resulting in significant IgM, IgG1, IgG2b, and IgA anti-SRBC plaque-forming cell responses when adoptively transferred to mice with OT. However, neither CD3+, CD4+, CD8-, nor double positive T cells affected OT when studied in this system. The CD3+, CD8+ IEL subset could be further separated into Thy-1+ (16.6%) and Thy-1- (83.4%) cells; adoptive transfer of Thy-1- cells abrogated oral tolerance whereas the Thy-1+ subset was without effect. When the expression of TCR on IEL with this biologic function was determined by use of monoclonal anti-alpha beta TCR (H57.597), TCR2-, CD3+ IEL possessed immunoregulatory function whereas the alpha beta-TCR+ (TCR2+) fraction did not abrogate OT. Immunoprecipitation of membrane fractions obtained from purified CD3+, CD4-, CD8+, Thy-1- IEL with polyclonal anti-delta peptide (Tyr-Ala-Asn-Ser-Phe-Asn-Asn-Glu-Lys-Leu) antibody revealed bands of 45 and 35 kDa, corresponding to the delta- and gamma-chains, respectively. These results suggest that gamma delta-TCR+ IEL possess a regulatory function, namely the restoration of immune responses in a state of oral tolerance. Further, both CD3+, CD4-, CD8+, Thy-1-, and CD3+, DN IEL T cells exhibit this effector contrasuppressor function.

Mucosal homeostasis: role of interleukins, isotype-specific factors and contrasuppression in the IgA response

Oral ingestion of antigen elicits immune responses at mucosal sites where humoral immunity is largely due to antibodies of the IgA isotype. This is often accompanied by suppression of systemic responses to the same antigen, a state termed oral tolerance. This IgA response is regulated by interactions between T cell subsets found at IgA inductive tissues, i.e., the gut-associated lymphoreticular tissue (GALT) or Peyer's patches (PP). PP T helper (Th) cells support IgA responses, and interleukins 5 (IL-5) and IL-6 can augment secretion of this isotype. Subsets of Th cells may also express Fc receptors for IgA (Fc alpha R) and secrete Fc alpha R as an IgA-binding factor (IBF alpha). Membrane-derived Fc alpha R is a glycoprotein of 38,000 M.W. and this molecule induces selective increases in IgA secreting cells (as determined by the ELISPOT assay) in PP B cell cultures. Fc alpha R+ T cell lines have been shown to secrete IBF alpha as well as IL-5 both of which promote IgA synthesis. Recombinant IL-5 (rIL-5) and rIL-6 induce IgA synthesis mainly by PP B cell blasts, and principally act on surface IgA-positive (sIgA+) B cells for these responses. Another form of mucosal regulation is provided by T contrasuppressor (Tcs) cells, which abrogate oral tolerance when adoptively transferred to mice and restore systemic responsiveness to the antigen sheep erythrocyte (SRBC). Tcs cells from mice systemically primed with SRBC support IgM and IgG subclass responses, while Tcs cells from orally primed mice support IgM, IgG subclass and IgA anti-SRBC responses. These Tcs cells are CD3+, CD4-, 8- and are antigen-specific. These regulatory cells may use the gamma-delta (gamma-delta) form of T cell receptor for antigen recognition.

Suppression of an established DTH response to ovalbumin in mice by feeding antigen after immunization

Experiments were designed to examine whether systemic delayed-type hypersensitivity responses (DTH) to ovalbumin (OVA) can be suppressed when antigen is fed after immunization, and to investigate the immunological mechanisms involved. A single 25 mg feed of OVA given 7 or 14 days after immunization with OVA in complete Freund's adjuvant (CFA) suppressed the DTH response of BDF1 mice, but had no significant effect on the serum IgG antibody response. DTH suppression was greatest when antigen was fed soon after immunization, and became less pronounced as the time interval between feeding and immunization increased. The phenomenon was also demonstrated in mice of the BALB/c strain. Cell transfer experiments suggested that the post-immunization suppression was not due to a population of suppressor cells that have been described previously in association with classical oral tolerance for DTH. We conclude that there are separate and distinct mechanisms for the prevention of induction of DTH by antigen feeding in naive mice and the suppression of expression of DTH in sensitized animals.

Irradiated mice lose the capacity to 'process' fed antigen for systemic tolerance of delayed-type hypersensitivity

'Intestinal antigen processing' is a function of the gastro-intestinal tract whereby shortly after an animal has been fed an immunogenic protein antigen, such as ovalbumin (OVA), a tolerogenic form of the protein is generated and can be detected in the circulation. The effect of damage to the intestinal epithelium on the processing of OVA has been examined in lethally irradiated mice. Irradiated animals were fed 25 mg OVA and their serum collected 1 h later. When this serum was transferred intraperitoneally into naive recipient mice, this did not induce the typical suppression of systemic delayed-type hypersensitivity. Results were similar when the serum donors were at 2 days after irradiation, with crypt hypoplasia, and at 5 days after irradiation when there was reactive crypt hyperplasia. However reconstitution of donors with normal spleen cells immediately after irradiation restored their capacity to generate a tolerogenic form of the antigen. Immunoreactive OVA was detected by ELISA in both tolerizing and non-tolerizing sera, and the immunological properties of these sera were not related to serum levels of OVA after feeding. Thus subtle immunochemical alterations in the nature of a protein antigen are likely to be more important than the quantity of absorbed antigen, in influencing systemic cell-mediated immune responses after feeding. The lack of generation of a tolerogenic form of the protein in irradiated mice, unrelated to the pattern of epithelial cell kinetics, and the restoration of this function by normal spleen cells, suggests that lymphoid cells may be involved in the phenomenon of antigen processing.

A genetically determined lack of oral tolerance to ovalbumin is due to failure of the immune system to respond to intestinally derived tolerogen

In this study we have examined whether differences between mouse strains in the induction of tolerance after feeding ovalbumin (OVA) are due to differences in intestinal processing of OVA or are determined by the systemic immune system. Compared with major histocompatibility complex (MHC)-congenic BALB/c mice, BALB/B mice develop much less tolerance of systemic delayed-type hypersensitivity (DTH) and humoral immunity after feeding OVA and this defect is also expressed partially in (BALB/B x BALB/c)F1 animals. Serum taken from either BALB/c or BALB/B mice fed OVA 1 h before produced significant suppression of systemic DTH responses in BALB/c, but not in BALB/B mice. Although OVA-fed BALB/B serum was slightly less tolerogenic than BALB/c serum, we conclude that the defective induction of oral tolerance in BALB/B mice is due primarily to a MHC-influenced defect with the immune system. These findings support the idea that clinical food-sensitive enteropathy reflects an immune response gene-controlled defect in tolerance to dietary proteins.

The influence of intestinal processing on the immunogenicity and molecular size of absorbed, circulating ovalbumin in mice

The presence of a tolerogen in mouse serum within 1 hr of antigen feeding prompted further study. Therefore, serum from mice fed with ovalbumin (OVA) was subjected to various immunochemical and biological tests. The appearance of tolerogen in serum was concomitant with the presence of OVA detected by a specific ELISA. Absorption of tolerogenic serum with anti-OVA antibody coupled to Sepharose beads effectively removed the tolerogenic moiety from the serum and confirmed that not only was tolerogenicity associated with the presence of antigen, but that binding sites for antibody were intact on this tolerogenic form of OVA. Finally, serum fractions from antigen-fed mice were assayed for total protein content, ELISA-detectable OVA and in vivo effect on systemic immunity. The only serum fraction in which immunoreactive OVA was detected contained proteins close to the molecular weight of native OVA and induced significant immune suppression in recipients. Serum fractions lacking immunoreactive OVA were not significantly tolerogenic in vivo. These experiments confirm that when OVA is absorbed across the gut mucosa it is subtly altered into a tolerogenic form. The recognition of gut-processed OVA by T-suppressor cells is discussed.

Selective effects of graft-versus-host reaction on disaccharidase expression by mouse jejunal enterocytes

Graft-versus-host reaction (GvHR) was induced in neonatal mice to produce crypt hyperplasia with and without stunted villi. Lactase activity was measured along individual villi of control and GvHR mice using quantitative cytochemistry. Lactase activity increased in control mice as enterocytes migrated over the lower part of the villus. This increase was followed by a period when lactase activity remained approximately constant. Effects produced by GvHR on this normal profile of development included an extension of the distance on the villus over which enterocytes could continue to increase lactase activity, a reduction in the time needed for an enterocyte to express lactase activity at maximal rate, and an overall decrease in the maximal lactase activity expressed by mature enterocytes. These effects have been quantified by fitting logistic curves to the experimental data. Parallel biochemical analyses of intestinal homogenates showed sucrase, isomaltase, trehalase and maltase activities to increase markedly 7-8 days after the injection of parental spleen cells. Attention is drawn to similarities between these results and steroid induced precocious development of intestinal function in neonatal mice.

Oral tolerance to ovalbumin in mice: studies of chemically modified and 'biologically filtered' antigen

Suppression of systemic immunity after the feeding of antigen was investigated in mice by means of serum transfer experiments. Serum collected from mice 1 hr after a single intragastric dose of 25 mg OVA induced suppression of systemic DTH when injected intraperitoneally into recipient mice. This suppression was found to be restricted to the cell-mediated limb of immunity and was antigen-specific. A postulated function of the intestine, conversion of antigen into tolerogenic form by means of intestinal antigen processing, was studied by attempting to mimic intestinal alteration of OVA by chemical modification of the antigen. Parenteral injection of mice with either deaggregated or denatured OVA did not produce the typical pattern of unresponsiveness seen in animals given intestinally processed OVA. Intestinal processing was also shown to be distinct from systemic antigen processing. Mice injected with serum containing systemically 'filtered' OVA did not become tolerant to OVA in the manner of recipients of serum from OVA-fed mice.