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Effect of Haemophilus influenzae polysaccharide outer membrane protein complex conjugate vaccine on macrophages
D M Ambrosino1, D Bolon, H Collard
1Laboratory of Infectious Diseases, Dana-Farber Cancer Institute, Boston, MA 02115.
Insights
The Haemophilus influenzae type b polysaccharide-conjugate vaccine PRP-OMPC uniquely increases spleen size and macrophage numbers in mice. This T cell-independent splenomegaly may enhance vaccine immunogenicity and explain its adjuvant properties.
Area of Science:
- Immunology
- Vaccinology
Background:
- Haemophilus influenzae type b polysaccharide-conjugate vaccines are crucial for infant immunity.
- The PRP-OMPC vaccine links polysaccharide to an outer membrane protein complex (OMPC) from Neisseria meningitidis.
- OMPC contains T cell epitopes and acts as an adjuvant, enhancing immune responses.
Purpose of the Study:
- To investigate the immunomodulatory effects of the PRP-OMPC vaccine beyond antibody production.
- To determine if PRP-OMPC induces splenomegaly and characterize the cellular changes involved.
- To explore the potential mechanism behind OMPC's adjuvant capacity.
Main Methods:
- Mice were immunized with PRP-OMPC or a control vaccine (oligosaccharide-diphtheria toxin conjugate) or saline.
- Spleen size and splenocyte counts were measured.
- Flow cytometry and immunohistochemical staining were used to identify cell populations (macrophages) and antigen expression (Mac-1, CD11C, MHC class II).
Main Results:
- PRP-OMPC immunization led to significant increases in spleen size and splenocyte number compared to controls.
- Flow cytometry revealed an increase in large splenocytes expressing Mac-1.
- Histology and immunohistochemistry confirmed an increase in red pulp and macrophages expressing Mac-1, CD11C, and MHC class II.
- Severe combined immunodeficient mice also showed PRP-OMPC-induced splenomegaly and increased macrophages.
Conclusions:
- PRP-OMPC vaccine induces T cell-independent splenomegaly characterized by an increased number of macrophages.
- This macrophage activation and potential cytokine release may contribute to PRP-OMPC's enhanced immunogenicity.
- The observed effects on macrophages could explain the adjuvant properties of OMPC.
Abstract:
Haemophilus influenzae type b polysaccharide-conjugate vaccines elicit protective antibody responses in young infants. One of these conjugates, polysaccharide linked to outer membrane protein complex (PRP-OMPC), is produced by linking the capsular polysaccharide to an outer membrane protein complex derived from group B Neisseria meningitidis. The outer membrane protein complex contains T cell carrier epitopes that elicit T cell-dependent antibody responses. OMPC also has been shown to increase the antibody response to other proteins administered concurrently that are not covalently linked (i.e., acts as an adjuvant). In this study PRP-OMPC immunized mice demonstrated significant increases in spleen size as well as in splenocyte number as compared to saline controls (p < 0.01, p < 0.001, respectively). No such increase was noted after immunization with another H. influenzae type b-conjugate vaccine, oligosaccharide linked to a variant of diphtheria toxin. By analytic flow cytometry, the mice immunized with PRP-OMPC demonstrated an increase in large splenocytes expressing the Ag Mac-1 (CD11b, CR3). Furthermore, the spleens on histologic examination were characterized by an increase in the red pulp area consisting predominantly of cells of macrophage morphology. By immunohistochemical staining, the cells were identified as macrophages due to expression of Mac-1 and p150,95 (CD11C) Ag. After PRP-OMPC immunization, severe combined immunodeficient mice also demonstrated significant splenomegaly with an increase in macrophages identified by expression of Mac-1 and MHC class II Ag. Thus PRP-OMPC vaccine resulted in T cell-independent splenomegaly with an increase number of macrophages. We propose that this unique property may confer increased immunogenicity to PRP-OMPC through macrophage activation and cytokine release. Furthermore, the effect on macrophages may explain the "adjuvant" capacity of OMPC.