Active Immunity for the USABO, Part 2 (will help you connect the dots if you’re reading Campbell’s immune chapter and are lost)
In Part 1, we left off on the process of Th, Tc, and B cell activation upon initial exposure to an antigen. This article will discuss how the body manages reinfection with the same pathogen.
During initial exposure, when active Th/Tc/B cells are created, cells corresponding to these activated cells, called memory cells, are created. There are memory B cells, memory Tc cells, and memory Th cells. Upon antigen re-exposure, all three kinds of memory cells are activated.
Memory B cells, which have “memory” of the antigen that prompted its creation, become plasma cells, which are the active version of B cells. Plasma cells create antibodies against the specific antigen. Another important thing to note about B cells, related to antibody production: I mentioned in the previous article that they can act as APCs. B cells are special: they are APCs that can only present the particular epitope (specific region of the antigen) they bind to. Other APCs are less selective. This is important to its function of antibody production, as technically, antibodies are targeted against epitopes, and not whole antigens. So this specificity makes sure that all the antibodies produced by a single B cell are against the exact same portion of an antigen.
Memory Tc cells become active Tc cells and do what Tc cells do. Same with memory Th cells: they become Th cells and activate Tc and B cells. Memory Th cells also activate memory Tc and B cells through cytokines.
Here’s a summary image. In part 1, I explained some direct cell activation mechanisms involving MHCs and stuff. If, in this picture, an arrow cannot be explained by the direct MHC-dependent stimulation, then it can be explained by cytokines: these are signaling molecules that activate immune cells.
Through the functions of memory cells, the body is able to avoid another dramatic immune response against the same pathogen. Vaccination takes advantage of this: when you get a vaccine, that’s your first exposure. You create memory cells. When you actually get infected with the pathogen, that’s your second. Your body knows how to handle it without you showing symptoms of infection.
kk bye read campbell idk
