Abstract
The cellular immune response elicited by Mycobacterium bovis Bacille Calmette-Guérin (BCG) has been carefully investigated, but the humoral immune response has been partially neglected. BALB/c mice were immunized with BCG strain used to immunize humans. Anti-BCG antibodies, as assayed by ELISA, began to appear in the sera after the third week of immunization and plateaued three weeks after the 8th immunization. The total immunoglobulins (Igs) were purified by caprylic acid method from pooled serum collected after the 8th immunization. Anti-BCG antigen antibodies were detected in the total Igs preparation as well as in IgG, IgM, IgA, IgG1, IgG2a, and IgG2b, but not in the IgG3. Distinct BCG proteins were recognized the IgGs in Western blot analysis. Opsonization of BCG bacilli by the purified Igs potentiated internalization of the bacteria by murine Raw 264.7 macrophages. The intracellular BCG elimination coincided with the induction of NO production, which was more pronounced in cells infected with opsonized BCG compared to those infected with the non-opsonized bacteria. Coincidently, the production of NO was also higher in macrophages infected with opsonized BCG (maximal NO production at 48 h of incubation). The obtained results demonstrate that repeated inoculations of BCG effectively activate the humoral immune response, justifying the use of BCG as a live recombinant vaccine vector to insert genes encoding virulence factors controlled by antibodies.
Highlights
Bacille Calmette-Guérin (BCG) is an attenuated strain of Mycobacterium bovis first used to vaccinate children with a high risk of acquiring tuberculosis (TB) [1]
Specific anti-BCG antibodies were quantified in the serum of immunized mice by enzymelinked immunosorbent assay (ELISA) assay using either rabbit anti-mouse total Immunoglobulin antibody or antibodies specific to different Ig classes (IgG, IgM, IgA, or the subclasses, IgG1, IgG2a, IgG2b and IgG3)
AntiBCG antibodies began to appear after the second immunization (n = 5; median = 8.8152 ± SD = 0.110642) compared with the sera collected before immunization (n = 5; median = 0.20712 ± SD = 0.079421)
Summary
Bacille Calmette-Guérin (BCG) is an attenuated strain of Mycobacterium bovis first used to vaccinate children with a high risk of acquiring tuberculosis (TB) [1]. BCG has become the most widely used vaccine, reaching 3 billion vaccinated individuals [2]. A meta-analysis of individuals vaccinated with BCG indicates that the risk of acquiring active TB is reduced by approximately 50 percent [3]. The observed presence of lipoarabinomannan on the BCG outer cell surface and the ability of this complex molecule to act as an immune adjuvant may increase the potential immunogenicity of BCG [8].
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