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T H 1 cells play an important role in classical macrophage activation as part of type 1 immune response against intracellular pathogens (such as intracellular bacteria) that can survive and replicate inside host cells, especially those pathogens that replicate even after being phagocytosed by macrophages. [45]
This cytokine—a class of signaling molecule [39] —kills cancer cells and cells infected by viruses, and helps to activate the other cells of the immune system. [ 40 ] In some diseases, e.g., the rare chronic granulomatous disease , the efficiency of phagocytes is impaired, and recurrent bacterial infections are a problem. [ 41 ]
Humans are home to 10 13 to 10 14 bacteria, roughly equivalent to the number of human cells, [2] and while these bacteria can be pathogenic to their host most of them are mutually beneficial to both the host and bacteria. The human immune system consists of two main types of immunity: innate and adaptive.
This is a list of [[White blood cell|immune cell], also known as white blood cells, white cells, leukocytes, or leucocytes. They are cells involved in protecting the body against both infectious disease and foreign invaders .
Stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses. [ 3 ] [ 4 ] Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells.
The innate immune system is always present at the site of infection and ready to fight the bacteria; it can also be referred to as the "natural" immune system. The cells of the innate immune system do not have specific responses and respond to each foreign invader using the same mechanism. [1]
Ten toll-like receptors have been described in humans. [26] Cells in the innate immune system have pattern recognition receptors, which detect infection or cell damage, inside. Three major classes of these "cytosolic" receptors are NOD–like receptors, RIG (retinoic acid-inducible gene)-like receptors, and cytosolic DNA sensors. [27]
In the phagolysosome, the cell attempts to use reactive oxygen species and acid to kill the bacterium. However, M. tuberculosis has a thick, waxy mycolic acid capsule that protects it from these toxic substances. M. tuberculosis is able to reproduce inside the macrophage and will eventually kill the immune cell.