Correlation of virulence, lung pathology, bacterial load and delayed type hypersensitivity responses after infection with different Mycobacterium tuberculosis genotypes in a BALB/c mouse model

Abstract

One of the most intriguing aspects of tuberculosis is that the outcome of an infection with M. tuberculosis (TB) is highly variable between individuals. The possibility of differences in virulence between M. tuberculosis strains or genotypes has only recently been studied. There is evidence of multifactorial genetic predisposition in humans that influences the susceptibility to tuberculosis. A better understanding of differences in virulence between M. tuberculosis genotypes could be important with regard to the efforts at TB control and the development of improved antituberculosis vaccines. Survival, lung pathology, bacterial load and delayed type hypersensitivity (DTH) responses of BALB/c mice after intratracheal infection with any of 19 different M. tuberculosis complex strains of 11 major genotype families were studied. The results indicate that among genetically different M. tuberculosis strains a very broad response was present with respect to virulence, pathology, bacterial load and DTH. 'Low'-responders were the H37Rv, Canetti, Beijing-1 strains, while Beijing-2,3, Africa-2 and Somalia-2 strains were 'high'-responders. A severe pathological response correlates with a high mortality and a high CFU counts in lungs, but poorly with the degree of the DTH response.

Fig. 1

Microscopic images of lung of mice 23 days after infection with Beijing-2 (a, b) and of mice 56 days after infection with Canetti (c) and with IS-in-Ori-1 (d). Examples are presented of the different lung pathological parameters and their score. In (a) a moderate peribronchiolar (score 3) (asterix) and perivascular (score 4) (arrow) infiltrate is present with some granuloma of moderate size (score 2). In panel b two marked granuloma (score 4) with areas of necrosis (asterix) surround a bronchiole. Slight perivascular infiltrate is present (arrow). In panel c only slight perivascular infiltrate (score 2) (arrow) and minimal alveolitis (score 1) (asterix) are present in this area, while in (d) a moderate perivascular inflammation (score 2) (arrow) is lying next to a small granuloma (score 2). HE, 60×. Bar = 100 µm.

Fig. 2

Score of lung pathology of mice 16, 28 and 56 days (and total score) after infection with 19 different M. tuberculosis strains. Strains are arranged with increasing pathology. From this figure it is clear that after infection pathology increases in time.

Fig. 3

Percentage of survival of mice infected with different M. tuberculosis strains. Beijing 3 infected animals did not survive 56 days.

Fig. 4

Colony forming unit-counts from lung tissue of mice at 3, 16, 23, 28 and 56 days after infection with different M. tuberculosis strains. Low (-----), moderate (——) and high (–·–·–·–) bacilarry load, can be discerned in time by their nearly horizontal lines from day 16.

Fig. 5

Delayed type hypersensitivity (DTH) responses one day after intracutaneous injection with H37Rv antigen in mice infected with different M. tuberculosis strains at 1, 3, 16, 23, 28 and 56 days after infection. With the exception of Less-transmissible 1 the highest DTH response was noted at day 23. Low (-----), moderate (——) and high (–·–·–·–) responders at day 16 are shown. Low responders remain the lowest during the experimental period, whereas the moderate and high responders show high variation at the other days postinfection.