Overview of immune system Part 4

Immune system

Continue adaptive immune defenses

Cellular defenses - T lymphocytes

Your immune system last efforts deploys when the  invaders made it to the cells, penetrated its membrane and started dividing, now it comes to a cell to cell combat.

T lymphocytes are one of your adaptive immune cells which originates in your bone marrow but matures in thymus gland, a lymphoid organ situated in your neck and becomes small by the time, puberty approaches, it secretes thymosin hormone stimulates the maturation & production of disease-fighting lymphocytes which are T-lymphocytes, there are kind of varieties of T-lymphocytes:

• Cytotoxic (killer) T cells, mainly kill/attack viruses, bacteria and infected host cells
• Helper T cells, they have a major role on your immune system, these cells are more likely to be the corner stone of the immune system, because of its presence, our immune system wouldn't have been able to identify & respond to any foreign antigens, these immune cells releases chemicals called ''Cytokines'' their secretions stimulates various things that contributes to your immune response: 

1. Activates macrophages from your innate immune system
2. Causes inflammation 
3. Helps in the maturation and activation of other immune cells such as B-lymphocytes to become plasma cells & present to it the specific antigen of the foreign invader from macrophages in order to produce the specific antibody for it.
4. Their chemical secretions induces other white blood cells to come to the                                     site of infection and increase the rate of white blood cells.    

                                                                                                                                                   

• Suppressor or Regulatory T cells, they have an important function in our immunity, they stop the immune processes when the infection is over in order to avoid any further production of immune cells or continuous immune responses which may lead to autoimmune diseases such as Multiple sclerosis where the white blood cells attack the myelin sheath surrounding the nerve cells or type one diabetes where the white blood cells attack pancreatic cells leading to the dysfunction in production of insulin also suppressor T cells induces plasma cells to save some cells having the information of the foreign invader ''Memory B cells'
• Memory T cells, which mainly has memories of the antigens of the specific invaders in case they made a comeback.
• Natural killer cell, these are of both types innate & acquired (adaptive) immune cells, they primarily attack infected-host cells by secreting messenger proteins containing ''Granzyme'' they are serine proteases ''enzymes that cleaves peptide bonds in proteins'' released by cytoplasmic granules within the cytotoxic T cells & natural killer cells they induces ''apoptosis'' (program cell death) that produces holes named perforins.

So this is how it goes, your macrophages from your innate immune system after engulfing a bacterium or virus they tend to present parts of these invaders on their outer layer on proteins found on the cell surface named major histocompatibility complexes of class (ll) these are professional antigen-presenting cells of class two such as macrophages, dendritic cells (=langerhans cells containing large organelles called Birbeck granules) and B-cells, dendritic cells, a major antigen-presenting cells binds to the antigens present on the macrophages they then travel to the nearest lymph node in about a day to bind with specific helper T cell which has a particular receptor for the specific antigen, once it binds it matures and start producing chemicals ''cytokines'' which calls for more white blood cells to get to the site of infection and divides producing memory T cells, regulatory T cells and killer T cells.

Thanks to the following websites and youtube channels for making this possible, if you find anything difficult send me your question in either my e-mail ahmed.maxi.93@gmail.com or just in the comments below I will be awaiting your feedback and we are finally done with Immune system episodes.

References used:
http://www.endocrineweb.com/endocrinology/overview-thymus
http://www.ebioscience.com/knowledge-center/cell-type/natural-killer-t-cells/granzymes.htm
https://en.wikipedia.org/wiki/Langerhans_cell
https://en.wikipedia.org/wiki/Phagocyte#/media/File:Dendritic_cell.JPG
https://www.youtube.com/channel/UCX6b17PVsYBQ0ip5gyeme-Q
https://www.youtube.com/channel/UCsXVk37bltHxD1rDPwtNM8Q

Dendritic cell under m

Diagram showing the binding of helper T cell with dendritic cell

This video explains  what is mentioned the above in a very simple way just in case you find something difficult to understand.