General Immune System

The Two Categories

This post will be the first in a series of three describing what comprises the immune system as well as how various drugs and medical procedures, particularly those related to transplantation (more specifically the kidney), affect it. A human’s immune system can be broken down into two main categories, innate immunity and adaptive immunity. The main cells that form the innate response are NK cells, complement proteins, dendritic cells, and macrophages which act as a form of constant surveillance for any antigens. This form of response is characterized by its rapid action and the fact that it’s antigen nonspecific. It is “activated” by chemicals released by damaged tissues (cytokines) and generally forms the the initial strike against the transplanted organ. A surgery can very well be described as a “carefully coordinated attack on the body” and these attacks during transplantations lead to many ruptured vessels and separated tissues all of which “call for help”. Though the innate response cannot lead to the rejection of a graft itself, it plays a large role in augmenting the adaptive immune response. The adaptive immune response comprises mainly of T-Cells and B-Cells. B-Cells have the job of producing antibodies, which are Y-shaped proteins which function to identify particular antigens (each one is specific to one type of antigen). T-Cells further divide into Cytotoxic T-Cells and Helper T-Cells. Helper T cells are arguably the most important to mounting an immune response as they help dictate what antibodies the B-Cells produce and also activate Cytotoxic cells to destroy the antigen. Though the adaptive response is much slower than the innate response, this is the one that ultimately leads to the destruction of the graft. Though it takes time for the correct antibodies to proliferate and for the T-Cells to target the kidney, it is a very specific attack on only those foreign cells, and it will continue until the failure of the graft (unlike the innate response which dwindles as the cytokines do). It is the careful and balanced suppression of this response that nephrologists (as well as cardiologists and gastroenterologists) seek for the survival of the graft.