The adaptive immune response is a specific defense mechanism of the immune system; it recognizes and targets specific antigens. There are two main branches of the adaptive immune system: humoral (antibody-mediated) immunity and cellular (cell-mediated) immunity. For this project, I will be focusing on the humoral immune response.
The first step of the humoral immune response is antigen presentation. Antigen-Presenting Cells (APCs; i.e., dendritic cells, macrophages, and B cells) engulf pathogens and present their antigen for lymphocytes to recognize. A T-helper cell, a lymphocyte used in the humoral immune response, meets with the pathogen and becomes partially activated. The partially activated T-helper cell binds to an antigen-presenting cell and becomes fully activated (Roche & Cresswell 2016). The fully activated T-helper cell binds to a B cell and releases cytokines, which activates the B cell. The activated B cell undergoes replication and differentiation, turning replicated B cells into Plasma B cells and memory B cells. Plasma B cells create and release antibodies, which mark antigens on pathogens for destruction (Alberts et al. 2002). Cytotoxic T cells recognize and bind to antibodies, which initiate an attack on the pathogen (Janeway et al. 2001). If the body becomes infected with the same pathogen again, Memory B cells hasten the immune response.
I’ve illustrated a comic series that demonstrates the humoral immune response in a fun way. The story begins when the antigen-presenting cell (APC) recognizes a foreign agent in the body. The virus sees the many cells surrounding it and wants to kill them. The helper T cell recognizes the foreign agent and asked the APC if he knew what it was. The APC expressed how he didn’t know but had the antigen from it. He asked the helper T cell to take it to the B cell so the killer cells can get to work. When the helper T cell reached the B cell, he attached the antigen to the B cell and released cytokines to initiate replication. The B cell processed the cytokines and replicated them into more B cells, the first differentiating into a memory B cell and the other into an antibody-producing plasma B cell. One of the B cells reminded the plasma B cell to spread the antibodies around so the killer cells can kill the virus. The plasma B cell throws the antibodies like kunai, the Japanese throwing knives. The antibodies found more viruses and started to bind to their antigens. The viruses began to panic, while one virus saw something strange in the background. Suddenly, the viruses got hit with a poisonous arrow, killing them instantly. Who did this? The cytotoxic T cell recognized the antibodies and shot two deadly arrows right at the weakest parts of the viruses. Mission accomplished!
Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Helper T Cells and Lymphocyte Activation. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26827/
Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. Chapter 9, The Humoral Immune Response. Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK10752/
Roche, P. A., & Cresswell, P. (2016). Antigen Processing and Presentation Mechanisms in Myeloid Cells. Microbiology spectrum, 4(3), 10.1128/microbiolspec.MCHD-0008-2015. https://doi.org/10.1128/microbiolspec.MCHD-0008-2015