This week in stem I continued by work on khan academy for biology. This week, I learned about the both the humoral and cell-mediated response. In both the humoral and cell-mediated responses occur after the foreign body or antigen has passed through the first line of defense. The first line of defense includes physical and chemical barriers that are always prepared to defend your body from infection. An example of first lines defenses are the skin and tears which prevent pathogens from entering your body. The humoral response occurs when the antigens are still outside of the cell, and the cell mediated response happens when antigens are inside of the cells. The difference between the two is what type of cell is activated. In the humoral response B-cells who have the ability to bind to free antigens bind to an antigen and then present it, or a piece of it, on a MHC two protein complex. When the protein is presented CD4+ T-cells, or helper T-cells, bind to the present peptide or antigen and fully activate the B-cell. Activated B-cells then divide in a process call colonial selection into memory cells or plasma cells. Memory Cells are long lasting cells that stay in the body to fight of the infection in the future. Plasma cells produce antibodies that “tag” the antigens for destruction. In the cell-mediated response, the antigen is in cells, which all have MCH I complexes that present things inside the cell so if the antigen is inside it will be presented. If the antigen is presented by an MHC I complex the CD4+ T-cell actives cytotoxic t-cells which can puncture the cell walls of infected cells and kill the viruses.

Next week in WISRD I want to review my learning to make sure that I fully understood it, and if possible want to start learning about the nervous system. I also want to keep up with the rocket group and help them with ideas and design.

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