TITLE:
Repeated inoculations of Mycobacterium bovis Bacille Calmette-Guérin (BCG) are needed to induce a strong humoral immune response against antigens expressed by the bacteria
AUTHORS:
Monique C. da Silva, Elena B. Lasunskaia, Wilmar Dias da Silva
KEYWORDS:
Mycobacterium bovis; Bacille Calmette-Guérin; BCG; Antibodies; Opsonization; Bacterial Killing
JOURNAL NAME:
Open Journal of Immunology,
Vol.3 No.3,
September
18,
2013
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.