Characterization of natural bactericidal antibody against Haemophilus influenzae type a in Canadian First Nations: A Canadian Immunization Research Network (CIRN) Clinical Trials Network (CTN) study

Invasive and Non-invasive Clinical Haemophilus influenzae Type A Isolates Activate Differentiated HL-60 Cells In Vitro

Background

The effective elimination of encapsulated bacteria like Haemophilus influenzae type a (Hia) relies on immune mechanisms such as complement-mediated opsonophagocytosis by neutrophils in coordination with opsonization by anti-capsular antibodies. This study evaluated if Hia could activate the immune response through neutrophils and if these responses differed between encapsulated versus unencapsulated or invasive versus non-invasive strains.

Methods

HL-60-derived neutrophil-like cells (dHL-60), differentiated with 1.25% dimethyl sulfoxide over 9 days, were used in an opsonophagocytosis assay and in vitro infection model to measure Hia's susceptibility to killing and dHL-60 surface molecule expression, respectively. The impact of strain-specific features on the immune response was investigated using clinical isolates of a dominant North American sequence type (ST)-23, including Hia 11-139 (encapsulated, invasive), 14-61 (encapsulated, non-invasive), 13-0074 (unencapsulated, invasive), as well as a representative ST-4 isolate (Hia 13-240, encapsulated, invasive), and a nontypeable strain (NTHi 375, unencapsulated, non-invasive).

Results

Unencapsulated and non-invasive Hi strains were more susceptible to killing by the innate immune response while the ST-23 invasive strain, Hia 11-139 required serum antibodies for destruction. Flow cytometry analysis showed increased expression of co-stimulatory molecule ICAM-1 and Fc receptors (CD89, CD64) but decreased expression of the Fc receptor CD16, revealing potential mechanisms of neutrophil-mediated defense against Hia that extend to both non-invasive and invasive strains.

Conclusions

Hia clinical isolates with diverse pathogenicity illustrated contrasting susceptibility to killing by immune mechanisms while maintaining the same capacity to activate neutrophil-like cells, further underscoring the need for additional studies on Hia's pathogenesis.

Naturally acquired antibody against Haemophilus influenzae type a in pediatric saliva

We developed a salivary assay for the detection of naturally acquired IgA antibody against Haemophilus influenzae type a (Hia) capsular polysaccharide in healthy Indigenous children from Northwestern Ontario, Canada. Hia-specific IgA antibody was detected in the saliva of 93% of Indigenous children aged 2-7 years.

Naturally acquired antibodies against 7 Streptococcus pneumoniae serotypes in Indigenous and non-Indigenous adults

Despite the use of pneumococcal conjugate vaccines for pediatric immunization, North American Indigenous populations continue to experience high burden of pneumococcal infections. Naturally acquired antibodies, which can protect unvaccinated adults against pneumococcal infections, have not previously been studied in Canadian Indigenous people. We analysed concentrations of natural serum IgG, IgM and IgA antibodies specific to 7 serotype-specific capsular polysaccharides (3, 6B, 9V, 14, 19A, 19F and 23F) in 141 healthy individuals (age between 18 and 80 years), including Indigenous adults living in 2 geographical different areas of Ontario, Canada, and non-Indigenous residing in northwestern Ontario. Regardless of the geographical area, concentrations of IgG specific to serotypes 6B, 9V, and 14, IgM specific to 9V, and all serotype-specific IgA were significantly higher in Indigenous study participants as compared to non-Indigenous. The differences are likely attributed to an increased exposure of Indigenous individuals to Streptococcus pneumoniae and/or cross-reactive antigens of other microorganisms or plants present in the environment. Although in non-Indigenous adults concentrations of IgM specific to 9V, 19A, 19F, and 23F significantly decreased with age, this was not observed in Indigenous individuals suggesting that Indigenous people may experience continuous exposure to pneumococci and cross-reactive antigens over the life span. Women had generally higher concentrations of natural IgG and IgM concentrations than men, with more striking differences found in Indigenous adults, potentially associated with larger exposure of women to young children, the major reservoir of pneumococci in communities. Our data suggest that increased rates of pneumococcal infections among Indigenous people are unlikely related to deficiency of naturally acquired antibodies, at least those specific to 7 common serotypes. Determining serological correlates of protection for adults will be essential to identify the groups in need of adult pneumococcal immunizations that may prevent excessive burden of the disease among North American Indigenous people.

Seroprevalence of IgG and IgM antibodies to Haemophilus influenzae type a in Canadian children

BACKGROUND

Over the last 2 decades, Haemophilus influenzae type a (Hia) has emerged as a significant cause of invasive disease in some geographic regions and populations. Recognition of the importance of Hia in the etiology of serious disease, particularly in young children, prompted the development of a new protein-capsular polysaccharide conjugate vaccine, similar in design to a vaccine against H. influenzae type b. At present, understanding of Hia immunology is incomplete; the immunological correlate of protection against invasive disease is unknown.

METHODS

Our objective was to study Hia antibody in children of various ages residing in a Canadian province with low incidence rates of invasive disease. The enzyme-linked immunosorbent assays were performed to quantify plasma IgG and IgM specific to Hia capsular polysaccharide in 133 children (3 months to 16 years).

RESULTS

Both anti-Hia IgG and IgM concentrations increased with age and were significantly higher in older children; a positive correlation between age and concentrations of Hia antibody was found. IgM antibody concentrations were significantly higher than IgG, with mean IgM concentrations over 10 times larger than IgG across all age groups.

CONCLUSIONS

The steady rise of naturally acquired, Hia-specific IgG and IgM concentrations in a pediatric population with low incidence rates of invasive Hia disease suggests the exposure to some cross-reactive environmental antigens as a major source of the antibody. However, the carriage rates of Hia in the region are unknown and further seroepidemiological studies are warranted. Although natural antibody may protect certain population groups against invasive disease, immunization of younger children will be essential to prevent serious infections if Hia continues to spread across North America.

Natural immunity against Haemophilus influenzae type a and B-cell subpopulations in adult patients with severe chronic kidney disease

Individuals suffering from severe chronic kidney disease (CKD) are immunocompromised and therefore highly susceptible to various infections including Haemophilus influenzae type a (Hia), an emerging pathogen in North American Indigenous populations. Immunocompromised Indigenous adults are considered a target for a new Hia vaccine under development. In an attempt to foresee their response to Hia immunization, we studied natural immunity against Hia and B-cell subpopulations in sixty patients with CKD residing in a geographic region with noticeable presence of Hia invasive disease. Serum bactericidal activity (SBA) against Hia, concentrations of IgG and IgM antibodies specific to Hia capsular polysaccharide, and B-cell subpopulations were studied in patients with CKD and 35 healthy controls of the same age. Of the patients with CKD, proportions and absolute numbers of B-cell subpopulations were determined for 28 patients. The patients had lower SBA titres compared to controls. Although no significant differences in anti-Hia IgG or IgM antibody concentrations between control and CKD groups were found, IgM antibody concentrations were higher in Indigenous than non-Indigenous patients. Patients with CKD had a higher proportion of B cells (CD19+), class switched memory B cells (CD19+CD27+IgM-) and a lower proportion of CD19+CD27-IgM- B cells compared to healthy controls. Non-Indigenous patients with CKD had significantly higher proportions of IgM memory B cells and CD19+CD27-IgM- B cells compared to Indigenous patients with no significant difference in absolute numbers. Because 72% of CKD patients had detectable SBA titres and 100% had detectable IgG and IgM antibodies it is possible that a portion of IgM memory B cells and class switched memory B cells are specific for Hia resulting from a natural exposure to the pathogen. The data suggest that a Hia-conjugate vaccine may be immunogenic in adult patients with CKD as it will potentially induce re-activation of immunological memory against Hia.