Adding Layers to my Understanding of Tuberculosis

When I teach medical students a concept my technique often involves reducing the concept down to the level of simple observation or unsophisticated laboratory or radiographic tests. This approach allows the medical student to not get lost in complexity and lose track of what's actually going on, namely a patient with certain signs or symptoms. 

As an avid attender of myriad infectious disease lectures I, myself, also tend to prefer this type of teaching approach. At a recent meeting of the Baltimore Tropical Medicine Dinner Club, on whose board I serve, I was treated to an exceptional employment of this very technique by an icon in the field of tuberculosis pathology: Johns Hopkins University's Dr. Arthur Dannenberg. 

What Dr. Dannenberg did in this lecture is reduce all the esoteric jargon of tuberculous pathology to literally entities visible to the naked eye (i.e. lesions on rabbit lungs). This lecture deepened my understanding of tuberculosis immensely because it provided me with a new framework to think about tuberculosis, namely as balancing act between two types of T-cell response. One type of response kills infected macrophages, the other activates macrophages to kill the bacteria. 

Using this paradigm it becomes much easier to understand why 90% of people are resistant to tuberculosis and never develop the disease after exposure. The infecting bacilli that survive the initial onslaught by alveolar macrophages are kept in check by a response which kills the cells that harbor them, creating a solid foci of necrosis surrounded by macrophage sentries poised to act. Most human's immune systems are able to keep this foci which, as it liquefies may leech out bacilli, in check (latent TB) but in those whose are unable, macrophages must release firepower on the area, causing the classic destructive lesions of tuberculosis. Aging and immunosuppression are two factor that can lead to loss of control and symptomatology. Similarly the poor population results of the BCG vaccine might be related to the fact that only a small proportion of the population actually needs it.

Such an understanding of tuberculosis provides a green light to think of therapy and vaccines differently. Primarily, tuberculosis therapy involves the prolonged use of antimicrobial therapy to kill bacilli in both the active and the latent stages. Therapies to keep the initial foci of necrosis from liquifying could modify therapy for latent TB. Additionally, immune modulation to dampen inflammation could also play a role (steroids are currently a part of the regimen used in tuberculous meningitis).

A proper conceptualization of a disease is really the only true means to understanding and conquering it.