PRIMING WITH Mycobacterium avium INCREASES IMMUNOGENICITY BUT NOT PROTECTIVE EFFICACY OF DNAHSP65 VACCINE

MARTINS D. R.(1,4), PELIZON A.(1,4), ZORZELLA S. F. (1,4), SEGER J.(1,4), JUSTULIN JR. L. A.(2), FONSECA D. M.(3), SILVA C. L.(3), MACHADO J. M. (4), SARTORI A.(1)

(1)Department of Microbiology and Immunology, Institute of Biosciences , UNESP, Botucatu, SP, Brazil; (2)Department of Morphology, IBB,  UNESP, Botucatu, SP, Brazil; (3)Department of Biochemistry and Immunology, FMRP, USP, Ribeirão Preto, SP, Brazil; (4)Department of Tropical Diseases and Diagnosis by Image, FMB, UNESP, Botucatu, SP, Brazil

The efficacy of BCG vaccine (attenuated Mycobacterium bovis) against pulmonary tuberculosis varies enormously in different populations. Previous studies have revealed that most protective antigens expressed by the antituberculous vaccine are conserved in M. avium, supporting the hypothesis that exposure to environmental mycobacteria generates a cross-reactive immune response that interferes with BCG efficacy. In this work we investigated the effect of a prior sensitization with heat killed M. avium on both, the immune response  and the protective efficacy induced by a DNAhsp65 vaccine (pVAXhsp65) in murine experimental tuberculosis. BALB/c female mice (6-8 weeks old) were used. Animals were initially, sensitized with 2x108 heat killed CFU of M. avium by subcutaneous route and then immunized with 3 doses of pVAXhsp65 (100mg/15 days apart) by intramuscular route. Control groups were injected with saline, pVAX (4 doses), pVAXhsp65 (4 doses), M. avium, M. avium plus pVAX (3 doses) or M. avium plus pVAXhsp65 (3 doses). Blood samples for antibody evaluation were collected 12 days after last DNA dose. Fifteen days after last DNA dose the animals were infected with 1x104 viable CFU of H37Rv M. tuberculosis by intratracheal route. Thirty days after challenge the animals were sacrificed and the bacterial burden was determined by the number of UFC in the lungs. Histological sections of lungs were also analysed. Priming with M. avium triggered a significant increase in the induction of IgG1 and IgG2a anti-hsp65 by pVAXhsp65 in comparison to all control groups. However this priming did not decrease the bacterial burden in the lungs. In addition, this prior sensitization with M. avium decreased the parenchyma preservation observed in the group immunized only with pVaxhsp65. These results reinforce the deleterious effect of environmental mycobacteria in antituberculous vaccines.

KEY WORDS: DNA vaccine, pVAXhsp65, mycobacteria, Mycobacterium avium

FINANCIAL SUPPORT: FAPESP, CNPq and CAPES

CORRESPONDENCE TO:

Alexandrina Sartori, Departamento de Microbiologia e Imunologia do Instituto de Biociências de Botucatu, UNESP, Caixa Postal, 510, CEP 18618-000, Botucatu, SP. Email: sartori@ibb.unesp.br