How does cellular immunity take place?

What are the steps that are taken for cellular immunity?

3 Answers

  • 1 decade ago
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    Cellular immunity is distinct from barrier immunity such as the skin, the mucosal tracts, lysozymes, pH of stomach acid etc. There are two main branches of cellular immunity: innate cellular immunity and adaptive cellular immunity.

    Innate immune cells circulate in the blood as monocytes after formation in the bone marrow and exit into the skin, spleen and the mucosal sites where they differentiate into macrophages and dendritic cells. These cells act as sentinels that will detect infection as soon as it penetrates the barriers of the skin and mucosa. They become activated and will begin to attack the infecting bacteria, fungi or viruses. They send out chemical signals called cytokines to reinforce the site of infection with neutrophils and later macrophages. The dendritic cells will leave the site of infection and enter the lymphatics to travel to the lymph nodes and activate the adaptive cells. There are also basophils, eosinophils and mast cells which are designed to detect and attack parasites and worms. They are also the cause of allergic reactions.

    Adaptive cellular immunity is found in the lymphnodes. Adaptive cells are the T cells (formed in the Thymus) and B cells (formed in the Bone Marrow and in birds the Bursa of Fabricus where they were first recognised). The lymphnodes act as the seives of the body's sewage system, the lymphatic system. B cells reside in the cortex, T cells constantly recirculate throughout all the lymphnodes in the body, ready to be activated anywhere from the toes to the brain. They are activated when dendritic cells, loaded with infectious particles exit the infected tissue and come into the lymphnodes via the lymphatics. Here they interact with and activate T cells. The T cells, depending on the mix of cytokines will transform into helper T cells which in turn activate B cells OR they transform into cytotoxic (Killer) T cells that will travel to the site of infection and kill infected cells.

    B cells once activated by helper T cells turn into plasma cells that make antibodies. These antibodies will be released into the circulation and seek out their target. They will bind to the bacteria or fungus or virus and will either cause it to clump and prevent it infecting further, or stop it binding to a cell to infect it or will bind it to macrophages and make that cell eat it up in the process of phagocytosis (and so destroy the bug).

    The important thing about adaptive immunity is that the T cells and B cells are able to recognise just about any molecular structure that may infect the body. But it takes longer to act, about 7 days to become fully functional, whereas innate cells are ready to react to common classes of bug instantly.

    They are able to do this because during their development, the genes for the receptors undergo shuffling that randomises their receptor. Those randomly formed receptors that recognise our own tissue are destroyed leaving only receptors that will recognise anything new and foreign. When they are activated, these cells undergo rapid division to make many millions of copies of themselves. Once they have attacked and destroyed the infection, a few of the T cells and B cells that were perfect matches for the infection are kept forever as memory cells. This ensures that if we catch that infection again, those T cells and B cells will be ready to react within hours so that we recover faster.

  • 5 years ago


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  • 1 decade ago

    I assume you mean organism immunity, right? One cell could have immunity like the waxy coating of tuberculosis to resist us, but our immunity is more complex.

    It starts with a memory cell or phagocyte encountering foreign matter and releasing interleukins to attract others. In short answer, our cells work together to mark what is dangerous with immunoglobin attached to the foreign cells' membrane bound surface structures used for recognizing each other. They are on the surface of the invading cells so they recognize each other in a colony to unite against the immune system, and are on the surface of viruses so they can attach to our cells and inject their DNA/RNA

    The overall picture is huge with several types of cells to fight in several different ways, because these foreign cells keep changing how their surface looks. I'd recommend you look up helper T cells, and read on from there. It's a long read, but not too hard to understand.

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