Study of respiratory symptoms among sputum positive

B) Delyed- type hypersensitivity (DTH)
Delyed type hypersensitivity (DTH) is immunologically the same
process as CMI, involving Th1- type T cells and their cytokines frequently
use. The terms tissue damaging DTH or cytotoxic DTH to represent the
immunologic reaction that causes caseous necrosis. Such necrosis develops
locally wherever, the tuberculin-like antigens form the bacillus reach
excessive concentration (Dannenberg, 1999). CMI and DTH immunologic
processes produced by the host play key roles in the pathogenesis of
tuberculosis (Dannenberg, 1991). The relationship between CM! and DTH
in the control offacultative intracellular microorganisms has been a subject
of debate for most of 20 th century. From a histologic study of the
tuberculous lesions and the bacillary growth curves it as apparent that both
CMI and DTH inhibit the multiplication ofthe tubercle bacillus equally
well. CMI does so, by activating macrophages to kill the bacilli they ingest.
Tissue damaging DTH does so by destroying bacilli-laden, non activated
macrophages and near by tissues there by eliminating the intracellular
environment that is so favorable for bacillary growth (Luri, 1964 and
Dannenberg, 1991).
Thus, the immune system ofboth tuberculin positive hosts with good
CM! and tuberculin positive hosts with poor CM! can arrest bacillary
growth. The host with poor eMI does so, however, with much damage to
its own tissues. Eventually, the host with good eMI may recover, but the
host with poor CMI dies from excessive tissue destruction (Dannenberg,
1999). Tissue-damaging DTH causing local necrosis stops the initial
.i. I bacillary growth within nonactivated macrophages. Which gives the host
time for eMI to develop local macrophage activation such cytotxic DTH
can never take the place of CMI because the bacilli that escape from the
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