Tuberculosis is one of the major health problems in the world and accounts for a large number of deaths. Statistics show that roughly one third of the world’s population is infected with the bacillus, and it is responsible for 8 to 12 million cases of active tuberculosis each year, and 3 million deaths [1. Raviglione M. C. 1995]. TB can be classified as being latent or active TB. Latent TB is described as the bacteria being present in the body but is inactive. The patient shows no symptoms and the bacteria are not contagious. Active TB is described as the bacteria being active in the body and the patient displays the symptoms and it also contagious [2. Young, L. S. 1993].
Derived from: www.who.int/healthtopicstuberculosis/en - map of cases of TB in the world
Tuberculosis is caused by the Mycobacterium tuberculosis (Mtb), a bacterium that is spread from one individual to the next via airborne particles. It is spread when an infected individual coughs, sneezes or spits so that the bacteria is released into the air and taken up by another individual. If the particles are inhaled it does not mean the person is infected immediately as one of three things can happen;
1. The body has a strong immune system which destroys the bacterium
2. The bacterium can remain as latent TB where the person has no symptoms and cannot spread it to others
3. The person becomes ill with TB
As mentioned before the Mtb is spread through the air and once the person inhales the bacterium it travels to the lungs where there are four different potential fates of the bacteria [3. Dannenberg A. M 1994]:
1. The initial response can completely eliminate the bacteria so that the patient does not develop TB in the future
2. The bacteria will begin to multiply and grow after infection and result in what is known as primary tuberculosis
3. The bacteria may become dormant and the patient does not even develop tuberculosis – here the patient has latent TB
4. The latent bacteria can eventually begin to multiply to result in reactivation tuberculosis.
Immunologic Responses to Mtb
The alveolar macrophage is the initial response to Mtb. The function of this cell is to inhibit the growth of Mtb through phagocytosis. It can also help with the cellular immunity through the process of antigen presenting to T-lymphocytes [4. Riley, L. 1996]. There are however, dendritic cells present in the airways but their exact roles in the defence against Mtb are not well known [5. Steinman R. M.1993]. Phagocytosis begins where that phagocytic cell engulfs the microbe in a tight membrane bound vacuole which has been created when pseudopods surround the bacterium and they fuse [6. Schlesinger L 1996]. This is called a phagosome. According to studies this vacuole is established by the binding of the bacterium to the phagocyte through complement receptors CR1, CR3 and CR4 as well as mannose receptors [6. Schlesinger L 1996]. The connection between Mtb and the mannose receptors on...