Dietary restriction abrogates antibody production induced by a DNA vaccine encoding the mycobacterial 65 kDa heat shock protein

Abstract

Background: Protein-calorie malnutrition (PCM) is the most common type of malnutrition. PCM leads to immunodeficiency and consequent increased susceptibility to infectious agents. In addition, responses to prophylactic vaccines depend on nutritional status. This study aims to evaluate the ability of undernourished mice to mount an immune response to a genetic vaccine (pVAXhsp65) against tuberculosis, containing the gene coding for the heat shock protein 65 from mycobacteria.

Methods: Young adult female BALB/c mice were fed ad libitum or with 80% of the amount of food consumed by a normal diet group. We initially characterized a mice model of dietary restriction by determining body and spleen weights, hematological parameters and histopathological changes in lymphoid organs. The ability of splenic cells to produce IFN-gamma and IL-4 upon in vitro stimulation with LPS or S. aureus and the serum titer of specific IgG1 and IgG2a anti-hsp65 antibodies after intramuscular immunization with pVAXhsp65 was then tested.

Results: Dietary restriction significantly decreased body and spleen weights and also the total lymphocyte count in blood. This restriction also determined a striking atrophy in lymphoid organs as spleen, thymus and lymphoid tissue associated with the small intestine. Specific antibodies were not detected in mice submitted to dietary restriction whereas the well nourished animals produced significant levels of both, IgG1 and IgG2a anti-hsp65.

Conclusion: 20% restriction in food intake deeply compromised humoral immunity induced by a genetic vaccine, alerting, therefore, for the relevance of the nutritional condition in vaccination programs based on these kinds of constructs.

Figure 1

Effect of dietary restriction on body (a) and spleen (b) weights. Weight values refer to day 1 (before dietary restriction) and days 10, 20, 30 and 40 after dietary restriction. Spleen weight refers to the 40^thday of dietary restriction. *Mean value was significantly different from that of the normal group (p < 0.05).

Figure 2

Effect of dietary restriction on lymphoid organs architecture and on hematological parameters. Thymus (a, b) and small intestine (c, d) sections stained with HE from BALB/c mice fed with normal diet (left column) or 80% of normal diet (right column). Total and differential number of monocytes, PMN cells and lymphocytes (e). *Mean value was significantly different from that of the normal group (p < 0.05).

Figure 3

Effect of dietary restriction on cytokine production by spleen cell cultures. IFN-γ (a) and IL-4 (b) levels were determined by ELISA in supernatants from cultures stimulated with Concanavalin A (ConA), lipopolysaccharide (LPS) and S. aureus (SAC) and non-stimulated cultures (basal). *Mean value was significantly different from that of the normal group (p < 0.05).

Figure 4

Effect of dietary restriction on antibody production induced by pVAXhsp65. Anti-hsp65 antibody production (IgG1 and IgG2a) was tested by ELISA in serum samples from BALB/c mice fed with normal diet (normal) or 80% of normal diet (restricted) groups. *Mean value was significantly different from that of the normal group (p < 0.05).