Effect of dietary factors upon the resistance of albino mice to experimental infection with Mycobacterium tuberculosis

The Need to Consider Context in the Evaluation of Anti-infectious and Immunomodulatory Effects of Vitamin A and its Derivatives

Vitamin A and its derivatives (retinoids) act as potent regulators in many aspects of mammalian reproduction, development, repair, and maintenance of differentiated tissue functioning. Unlike other vitamins, Vitamin A and retinoids, which have hormonal actions, present significant toxicity, which plays roles in clinically relevant situations, such as hypervitaminosis A and retinoic acid ("differentiation") syndrome. Although clinical presentation is conspicuous in states of insufficient or excessive Vitamin A and retinoid concentration, equally relevant effects on host resistance to specific infectious agents, and in the general maintenance of immune homeostasis, may go unnoticed, because their expression requires either pathogen exposure or the presence of inflammatory co-morbidities. There is a vast literature on the roles played by retinoids in the maintenance of a tolerogenic, noninflammatory environment in the gut mucosa, which is considered by many investigators representative of a general role played by retinoids as anti-inflammatory hormones elsewhere. However, in the gut mucosa itself, as well as in the bone marrow and inflammatory sites, context determines whether one observes an anti-inflammatory or proinflammatory action of retinoids. Both interactions between specialized cell populations, and interactions between retinoids and other classes of mediators/regulators, such as cytokines and glucocorticoid hormones, must be considered as important factors contributing to this overall context. We review evidence from recent studies on mucosal immunity, granulocyte biology and respiratory allergy models, highlighting the relevance of these variables as well as their possible contributions to the observed outcomes.

Impact of Vitamin A and Carotenoids on the Risk of Tuberculosis Progression

BACKGROUND

Low and deficient levels of vitamin A are common in low- and middle-income countries where tuberculosis burden is high. We assessed the impact of baseline levels of vitamin A and carotenoids on tuberculosis disease risk.

METHODS

We conducted a case-control study nested within a longitudinal cohort of household contacts (HHCs) of pulmonary tuberculosis case patients in Lima, Peru. We defined case patients as human immunodeficiency virus (HIV)-negative HHCs with blood samples in whom tuberculosis disease developed ≥15 days after enrollment of the index patient. For each case patient, we randomly selected 4 controls from among contacts in whom tuberculosis disease did not develop, matching for sex and year of age. We used conditional logistic regression to estimate odds ratios for incident tuberculosis disease by vitamin A and carotenoids levels, controlling for other nutritional and socioeconomic factors.

RESULTS

Among 6751 HIV-negative HHCs with baseline blood samples, 192 had secondary tuberculosis disease during follow-up. We analyzed 180 case patients with viable samples and 709 matched controls. After controlling for possible confounders, we found that baseline vitamin A deficiency was associated with a 10-fold increase in risk of tuberculosis disease among HHCs (adjusted odds ratio, 10.53; 95% confidence interval, 3.73-29.70; P < .001). This association was dose dependent, with stepwise increases in tuberculosis disease risk with each decreasing quartile of vitamin A level.

CONCLUSIONS

Vitamin A deficiency strongly predicted the risk of incident tuberculosis disease among HHCs of patients with tuberculosis. Vitamin A supplementation among individuals at high risk of tuberculosis may provide an effective means of preventing tuberculosis disease.

Influence of vehicles used for oral dosing of test molecules on the progression of Mycobacterium tuberculosis infection in mice

Preclinical evaluation of drug-like molecules requires their oral administration to experimental animals using suitable vehicles. We studied the effect of oral dosing with corn oil, carboxymethyl cellulose, dimethyl sulfoxide, and polysorbate-80 on the progression of Mycobacterium tuberculosis infection in mice. Infection was monitored by physical (survival time and body weight) and bacteriological (viable counts in lungs) parameters. Compared with water, corn oil significantly improved both sets of parameters, whereas the other vehicles affected only physical parameters.

Effects of protein intake on immune parameters in mice surviving streptococcal infection

Groups of mice were fed for 2 weeks on isocaloric diets containing 5, 7, 20 and 40% (w/w) casein, respectively, then injected intraperitoneally with group B streptococci, and observed for their survival rates. The mice fed 7% or 20% casein had lower mortalities than those fed 5% or 40% casein. In order to explain the different survival rates, other groups of mice were fed on the experimental diets and examined for the number of leukocytes in the blood, of spleen cells and thymocytes, for IgG and IgM antibody titres to the streptococci, for haemolytic titres of sera, the amount of complement component 3 (C3), for chemiluminescence and opsonic activity of peritoneal exudate cells (PEC) and spleen cells (SP), production of superoxide anion from PEC and SP, and production of immunoglobulins from cultured SP. After 2 weeks on a 7 or 20% casein diet mice showed increased serum levels of IgM antibodies reactive with the whole bacterial cells on days 3-5 when they were immunised with a sublethal dose of group B streptococci. The mice fed on the 7% casein diet also showed a higher C3 titre than the other diet groups when assayed by enzyme immunoassay. Furthermore, opsonophagocytic activity was highest when PEC or SP taken from mice on the 20% case in diet were incubated with radiolabelled microorganisms in the presence of fresh serum taken from the 7% casein group. The production of superoxide anions from PEC and SP was lowest in the mice fed on 5% casein when activity was expressed as nano-mol per animal. It is suggested from these results that the greater activity of phagocytic cells in the presence of increased amounts of C3 and IgM explains the heightened resistance in the mice fed on a 7% casein diet, and that suppressed opsonophagocytic activity resulting from the decreased number of leukocytes in the blood and other phagocytic cells explains the lowest resistance in the 5% casein group. However, mice fed on a 40% casein diet showed all these immunological parameters untouched, and their lowered resistance could not be explained. Different factors seem to be operative in them.

Quantitative pathologic study of avian tuberculosis in the chick. Effect of protein and lysine dietary levels

Images