The spectrum of infection with M. tuberculosis ranges from rapidly progressing overt TB to asymptomatic containment. M. avium is a human pathogen in the absence of the normal T cell response which causes death in patients with advanced AIDS or chronic lung disease on the background of less impaired immunity. This wide range is likely due to differences in the ability of genetically different hosts to develop protective innate and acquired immune responses. How these responses are regulated at genetic and cellular levels remains largely unknown. Many aspects of genetics and immunity to mycobacterial diseases has proven to be extremely difficult to study in humans, due to the complexity of host genetics, variations in the microbe determinants and the level of exposure. A recent workshop organized by the NHBLI made animal models its first recommendation. We developed a range of murine models of M. tuberculosis and M. avium infections with very similar pathological features, and demonstrated a mirror-type susceptibility/severity pattern for two infections in B6 and I/St inbred mice - a unique, self-controlling experimental setting. We propose to combine DNA microarrays, real time PCR, immunohistochemistry, antibody therapy and gene mapping approaches to: (i) investigate the shifts in host gene expression that accompany development of M. tuberculosis and M. avium infections in genetically susceptible and resistant mice;(ii) evaluate the features of lung pathology in these animals, (iii) apply anti-neutrophil and anti-IL-11 immunotherapies in order to decrease pathology;and (iv) dissect the role of individual QTL and MHC genes in the control of infection. Evaluation of gene expression profiles in lungs and lymphoid organs will lead to a better understanding of the changes in gene expression that differentiate between effective vs. impaired host defense mechanisms. Using immunohistochemistry, we will further dissect phenotypic differences by studying the dynamics of trafficking of lymphoid cells to infectious foci and the architecture of lung pathology, i. e., granuloma formation, hypoxification and necrotization. We will apply therapies with antibodies in order to modulate development of lung pathology. To analyze the impact of QTL involved in TB control, we developed a panel of mouse strains congenic for individual Chr. 3 and 9 QTL. These new mouse strains will be studied with respect to the TB susceptibility. If contrast phenotypes are expressed, we will define the QTL map locations to approximately 1-2 cM intervals by a sequential 2-stage interval-specific approach. Next, we will clone corresponding QTL relying on testing of candidate genes available from complete mouse gene map. If the difference at a single QTL does not provide a reliable phenotype, we will produce a panel of double-congenic strains for Chr. 3 and 9 QTL in order to define epistatic/complementary interactions between QTL.
Our aim is to increase knowledge of the biology of M. tuberculosis and M. avium infections in general and specifically the gene expression profiles associated with susceptibility or resistance, development of lung tissue pathology and genetic control of infections in mouse models. This is an important step to understanding the disease in humans. Much of the information gained can then be translated to the human situation and used to derive improvements in health, such as better drugs and vaccines.
