Tuberculosis: The Microbe Host Interface Chapter Abstracts
Chapter 1
M. tuberculosis Entry and Growth using Macrophage Models
Zahra Toossi and Larry S. Schlesinger
Abstract
Although the central role for mononuclear phagocytes in the pathogenesis of tuberculosis has
been known for a century, the resurgence of tuberculosis in the United States and worldwide over
the past two decades has lead to an equally impressive resurgence of research aimed at further
defining the molecular events underlying many aspects of the
M. tuberculosis (MTB)-mononuclear phagocyte interaction. This chapter summarizes recent advances and compares various in vitro and in vivo models, pointing out strengths and weaknesses. It is clear that monocytes and macrophages differ phenotypically and functionally among mammals and between tissue compartments of the
human host in ways that impact on the host response to MTB.
Chapter 2
Analysis of Post-Phagocytic Events: Membrane trafficking and the
Mycobacterium tuberculosis phagosome
Daniel L. Clemens
Abstract
Mycobacterium tuberculosis subverts the normal membrane trafficking pathway of the host cell:
it prevents the maturation and acidification of its phagosome, and thereby achieves a phagosome
that is hospitable for its growth. The composition of the phagosome and the interactions between
the phagosome and other host cell organelles have been studied by a variety of different
techniques, including transmission electron microscopy, immunoelectron microscopy,
immunofluorescence microscopy, and biochemical and immunological analysis of isolated phagosomes. In addition,
the pH of the phagosome has been studied both by fluorescence and electron microscopy
based techniques. Each of these methods for characterizing the properties and the membrane
trafficking interactions of the M. tuberculosis phagosome has advantages and disadvantages, and each
technique has the capacity to complement the other techniques in providing a more complete picture of
the composition and membrane trafficking interactions of the
M. tuberculosis phagosome.
Chapter 3
Analysis of Macrophage Signaling Following
M. tuberculosis Infection
David J. Kusner
Abstract
Mycobacterium tuberculosis with human macrophages are central to
all aspects of the pathogenesis of tuberculosis, from initial infection to reactivation disease.
Characterization of the biochemical mechanisms by which macrophages respond to
M. tuberculosis has provided exciting insights into pathophysiology and will foster unique approaches for therapy and prevention. This chapter will outline the macrophage
signal transduction pathways that regulate two critical phases of the host-pathogen interaction
in tuberculosis; phagocytosis and phagosome maturation. In addition to reviewing our
current understandings and gaps in knowledge, emphasis will be placed on the experimental
approaches that are currently employed, as well as those emerging technologies that are beginning to
inform our studies of mycobacterial pathogenesis.
Chapter 4
The Acquired Immune Response to
M. tuberculosis
W. Henry Boom
Abstract
M. tuberculosis remains one of the most successful human pathogens. The ability of M. tuberculosis to elicit vigorous acquired immune responses and use of the macrophage as primary cell to infect, suggest that the organism has evolved multiple strategies to survive and persist in the face of
innate and acquired immune responses. Persistence of
M. tuberculosis in otherwise healthy persons is one of the hallmarks of this organism. Survival and persistence require not only resistance to
microbicidal mechanisms of phagocytes but also avoidance of recognition by multiple T cell subsets. The
acquired immune response to M. tuberculosis requires participation by multiple T cells subsets. These
include not only a central role for MHC-II restricted CD4+ T cells, but also MHC-I restricted CD8+,
gamma-delta and CD-1 restricted T cells. These diverse T cell populations recognize a wide range
of mycobacterial antigens, but share overlapping functions such as secretion of
IFN-g and TNF-a, CTL function, and ability to provide cell-contact dependent help to macrophages. How T
cell responses are regulated in vivo and their roles in different stages of M. tuberculosis infection and in protective immunity remain to be determined. Answers to these questions will impact vaccine development as well as understanding the host-pathogen interaction in
M. tuberculosis infection.
Chapter 5
New In Vitro Models of Mycobacterial Pathogenesis
Frederick D. Quinn, Luiz E. Bermudez and Kristin A Birkness
Abstract
Mycobacterium tuberculosis bacilli are inhaled into the lung, eventually reaching the alveoli
where the organisms are ingested by alveolar macrophages. If not killed by these macrophages, the
bacilli replicate intracellularly and spread to other alveolar and recruited macrophages. Within weeks,
a few bacilli can multiply to significant numbers and infect hundreds or thousands of alveolar
cells. Subsequent dissemination of these infected macrophages from the alveoli into the lymph
and circulatory systems may be critical to the establishment of active and latent disease. This
simple view of a complex process describes the diverse environments in which the mycobacteria
must compete in order to survive, replicate and ultimately disseminate. This view also illustrates
the daunting task facing investigators who are attempting to dissect and analyze each of the
steps employed by the pathogen and host. Several model systems are now available to help
investigators elucidate several aspects of the
M. tuberculosis pathogenesis process. Although the animal and tissue culture monolayer models are the most widely used, a third system, complex
in vitro models are beginning to be utilized. What we describe here are a number of these model systems and how they are or could be used to examine many of the stages of the infectious process.
Chapter 6
Animal Models in the Analysis of Pathogenesis.
Andrea M. Cooper
Abstract
The pathogenesis of tuberculosis is a complex process that depends upon components of both
the vertebrate host and the mycobacteria. Animal models are required to address the complexity of
the interactions between host and pathogen. In their own right they can be used to address
hypotheses regarding the role of individual components in pathogenesis but the real strength of the models
lies in the use of comparative pathology. Comparing and contrasting the responses of several
animal models of tuberculosis can result in the development of novel hypotheses regarding
pathogenesis of this disease. This development may lead to a greater understanding of the pathogenic
process and thus a greater ability to create effective immune mediated interventions such as vaccines
that not only induce anti-bacterial effector functions but also help to limit the pathologic consequences of disease.
Chapter 7
Analysis of Mycobacterium tuberculosis Gene Expression in the Human Host
Josephine E. Clark-Curtiss and Lucy E. DesJardin
Abstract
Survival and growth within the human host are essential elements of
Mycobacterium tuberculosis pathogenesis. Thus, understanding the physiology of the tubercle bacilli within the infected host will enable investigators to define the mechanisms of pathogenesis of this organism. In this
chapter, we summarize the approaches that have been and are being used to analyze mycobacterial
gene expression during its sojourn in the human host, as well as the knowledge that has been gleaned
in our understanding of this very successful pathogen.
Chapter 8
Analysis of Latency
John Chan and JoAnne Flynn
Abstract
Reactivation of latent tuberculous infection plays a significant role in the pathogenesis of
tuberculosis. The mechanisms involved in the establishment of latent tuberculosis and subsequent
recrudescence are, however, not well understood. Studies designed to characterize these
mechanisms have been hampered by the lack of knowledge of the precise immunologic response of the host
as well as the physiologic state of the tubercle bacilli during latent and reactivation tuberculosis,
thus rendering modeling of these two phases of tuberculous infection difficult. Nonetheless,
results obtained through the use of various in vitro and in vivo models have shed considerable light on
the host-bacillus interaction in latent and reactivation tuberculosis.
Chapter 9
Molecular Epidemiology: Clinical Utility, Public Health Implications and Relevance
to Pathogenesis
Peter F. Barnes and M. Donald Cave
Abstract
We review the advantages and disadvantages of the most widely used methods for genotyping
M. tuberculosis. The current gold standard is based on the distribution of the insertion sequence IS6110, but genotyping based on polymorphism of mycobacterial interspersed repetitive units is a promising technology that provides automated, high-throughput results that can be expressed digitally
and easily compared. Genotyping allows the clinician to identify cases of laboratory
cross-contamination, and assists in treatment of patients with recurrent tuberculosis and those whose isolates show
different drug susceptibility patterns. Population-based genotyping has major public health
implications, demonstrating that recent transmission contributes significantly to tuberculosis morbidity
and identifying subpopulations in which ongoing transmission is a problem. In locations
where tuberculosis case rates are high, surveillance genotyping has the potential to identify and limit
the spread of unsuspected tuberculosis outbreaks. Molecular epidemiologic studies have revealed
several critical features about the pathogenesis of tuberculosis. First, some strains are much more
widely distributed than others, suggesting that they have phenotypic characteristics that favor
dissemination. Second, drug-resistant strains may be less transmissible than drug-susceptible ones,
suggesting that some genes that encode for drug resistance also decreased fitness. Third, prior
tuberculosis does not protect against new disease from exogenous reinfection, suggesting that effective
vaccination must do more than mimic natural infection.