Protective immunity to chronic bacterial infection

Vaccines against mycobacteria and other intracellular multiplying bacteria

As the prototype of a vaccine against mycobacterial infection, the BCG (bacille bilié Calmette et Guérin) has been used against tuberculosis for more than 60 years. It is the only live attenuated vaccine used on humans in more than 182 countries or territories in the world, and very few changes have been made in its fabrication and distribution, except for the production of lyophilized seed-lots. However, its history is marked with controversies concerning its innocuity and efficacy. While BCG safety is no longer a matter of debate, the question of its effectiveness is still pertinent, and results in several controlled trials have shown great variability (from 0 to 80%). The studies of different variables involved in such results have shown statistical bias, and numerous factors are involved in the highly complex interrelationships between the host, the pathogen and environmental factors. World-wide research is now being conducted under the auspices of the World Health Organisation, in order to gain further knowledge of the immunology of tuberculosis and leprosy. Such results are aimed at understanding variations in BCG efficacy and producing strategies for developing new vaccines and alternative methods for prophylaxis and diagnosis. Concerning human infections due to other facultative intracellular multiplying bacteria, there are relatively few vaccines which are able to give long-lasting and efficient protection. Some controversy remains as to the live attenuated mutant GalE S. typhi Ty21a, and there is hope for the new insoluble phenol extract from Brucella abortis, strain B19. Further research is necessary on the others, for instance, Listeria monocytogenes, Chlamydia trachomatis and Legionella sp.

Natural resistance to mycobacteria: antimicrobial activity and reactive oxygen intermediate releasing functions of murine macrophages

After infection with Mycobacterium lepraemurium or with M. bovis strain BCG (bacillus Calmette-Guérin), splenic macrophages from mice naturally resistant (NR) to these pathogens (C3H and A/J) spontaneously produced H2O2, whereas splenic macrophages from naturally susceptible (NS) mice (C57BL/6 and Swiss) did not. None of them produced superoxide anion O2-. In addition, NR macrophages had higher levels of superoxide dismutase (SOD) than did NS macrophages. In vivo treatments thought to enhance H2O2 metabolism (phorbol myristate acetate, SOD, Zymosan) decreased M. lepraemurium survival, whereas treatment with diethyl-dithiocarbamate, a potent inhibitor of SOD, had the converse effect. These results favour the hypothesis of a link between natural resistance to BCG (and M. lepraemurium) and H2O2 metabolism, with higher producers being naturally resistant.

Abnormalities in cell-mediated immune functions to Haemophilus influenzae chronic purulent infections of the upper respiratory tract

Delayed hypersensitivity (dh) skin test reactivity to a somatic antigen of Haemophilus influenzae was studied in 21 patients with unexplained, chronically relapsing, purulent upper respiratory tract infections. Only 2 showed a dh reactivity comparable to that of healthy controls. A majority--15 patients--had a defective dh response, whereas 4 showed exaggerated reactivity leading to necrosis of the test site and general feelings of malaise. Not only was the dh reactivity to somatic H. influenzae antigen affected, but also that to streptokinase/streptodornase and candidal antigen in most cases, though to a lesser extent. Skin test reactivity to the mitogen PHA was normal as were the dh skin test reactivities in 4 out of 5 control patients with mucous atopic rhinitis/sinusitis and 2 cases of nasal suppuration due to disturbed mucociliary transport. Delayed hypersensitivity skin test disorders were associated with elevated ratios of OKT4 + /OKT8 + peripheral lymphoid cells. In addition a high incidence of atopy and thyroid autoimmunity was evident in patients as well as in their first-degree relatives. A negative lymphocyte proliferative response to somatic H. influenzae antigen was found in 3 of our patients. These results suggest that unexplained, chronically relapsing upper respiratory tract infections might be based on restricted T-cell defects to H. influenzae, streptococcal, and candidal antigens. Such defects are reminiscent of the T-cell immune disorders to fungi playing a role in some cases of chronic mucocutaneous candidiasis.