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Antibodies to Haemophilus influenzae type b polysaccharide affect bacterial adherence and multiplication
L van Alphen1, P Eijk, H Käyhty
1Department of Medical Microbiology, University of Amsterdam, The Netherlands.
Insights
Anti-Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) antibodies inhibit bacterial growth but show limited efficacy in preventing adherence to nasopharyngeal cells. This suggests a dual mechanism for Hib colonization control.
Area of Science:
- Immunology
- Microbiology
- Vaccinology
Background:
- Infant immunization with conjugated Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) vaccines effectively reduces Hib colonization.
- Understanding the precise mechanisms by which anti-Hib PS antibodies impact colonization is crucial for vaccine development.
Purpose of the Study:
- To investigate the inhibitory effects of anti-Hib PS antibodies on two key steps of H. influenzae colonization: adherence to nasopharyngeal epithelium and bacterial growth.
- To evaluate the efficacy of a specific monoclonal antibody (MAb) and sera from immunized children against Hib adherence and growth.
Main Methods:
- In vitro assessment of monoclonal antibody E117-5's effect on Haemophilus influenzae (Hib) strain 770235f+b+ adherence to oropharyngeal epithelial cells.
- Evaluation of the inhibitory potential of MAb E117-5 and human sera from Hib PS conjugate vaccine recipients on Hib growth.
- Comparison of inhibitory effects against encapsulated Hib strain 770235f+b+ and nonencapsular variant strain 770235f+b0.
Main Results:
- Monoclonal antibody E117-5 significantly inhibited Hib adherence to epithelial cells by 50% at concentrations of 80 microg/ml (P < 0.02).
- Neither MAb E117-5 nor sera from immunized children showed significant inhibition of adherence at concentrations up to 20 microg/ml.
- Complete inhibition of Hib strain 770235f+b+ growth was observed with 5 microg/ml of MAb E117-5 and 2 microg/ml of anti-Hib PS in human sera, unlike the nonencapsular variant.
Conclusions:
- Anti-Hib PS antibodies demonstrate potent bactericidal activity, effectively halting bacterial growth.
- The inhibitory effect on adherence is less pronounced, suggesting that while antibodies can stop growth, they may not fully prevent initial attachment to the nasopharyngeal epithelium.
- These findings highlight the multifaceted role of anti-Hib PS antibodies in controlling H. influenzae colonization.
Abstract:
Since immunization of infants with conjugated Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) vaccines results in a reduction of colonization, we determined the inhibitory effect of anti-Hib PS on two steps in the colonization, i.e., adherence of H. influenzae to nasopharyngeal epithelium and bacterial growth. Monoclonal antibody (MAb) E117-5 specific for Hib PS inhibited at a concentration of at least 80 microg/ml in vitro the adherence of Hib strain 770235f+b+ to oropharyngeal epithelial cells by 50% (P <, 0.02), but this MAb and sera from children immunized with Hib PS conjugate vaccine (n = 10) were not inhibitory in final dilutions containing up to 20 microg of anti-Hib PS per ml. The growth of Hib strain 770235f+b+ did completely stop in the presence of 5 microg of anti-Hib PS MAb E117-5 per ml and human sera with an anti-Hib PS concentration of 2 microg/ml or more, in contrast to the growth of the nonencapsular variant strain 770235f+b0.