Post for October 6th

I've got a really busy weekend so I'm going try and post for Monday today. Because chapter 8 is so huge, I am just going to blog on the first segment, the innate immune response segment, in order to maintain some semblance of following the 3 sentence guidelines.

1. The first section begins by identifying the broad classes of possible infections (virus, bacteria, fungi, parasites) and then continues to identify the different parts of the immune system which combat them. First there is epithelial tissue, which provides a physical barrier of protection against invading agents and has chemical defenses as well (lysozyme in tears and saliva, acid and hydrolytic enzymes in the stomach, and antimicrobial peptides called defensins, which are found on all epithelial surfaces), finally, non-pathogenic flora inhabit many epithelial tissues and compete with possible pathogens for space and nutrients in a defensive way. The next line of defense are complement proteins which can work with antibodies to opsonize pathogens so they may be phagocytosed by macrophages, the next main line of defense. Macrophages are long lived, matured monocytes which inhabit connective tissues and phagocytose pathogens and release cytokines which recruit other cells to defend their tissue, causing a state of inflammation; they are guided by complement proteins and also by the adaptive immune cells. Another, primary, form of the innate immune response are the neutrophils, which are short lived and circulate in the blood, waiting for an inflammatory mediator signal from a tissue to bring them to the site of infection where they will phagocytose microorganisms and kill them with a collection of damaging chemical agents--primarily toxic oxygen radical species. The chapter continues to tell the functions of various excreted cytokines and of NK Cells which are a third form of immune lymphocyte which can be stimulated to very effectively kill invading cells and release cytokines.

2. The main challenge of this chapter for me was its sheer magnitude. I have above summarized only perhaps 1/4 of the main ideas in the chapter, and at only 1/8 the detail! Some mechanisms also came across a bit foggy to me; macrophages seem to recognize pathogens for phagocytosis with some fairly generalized receptors, if macrophage receptors dont have the same genetic variation as the adaptive immune cells how can they recognize pathogens without also being self reactive? If macrophages can use these more general and yet still not self-antigen receptors to kill invaders, why the need for the highly specialized adaptive immune system?

3. I found this chapter very enlightening with respect to the physical organization of all of these immune cells within the body, and this physical organization really helped me to learn each cell types particular functions. The distinction between the blood stream and outer tissues is a big one and I found these environments helped me to understand how and why different cells exist in different places (lower numbers of long lived, effector-cell-recruiting macrophages in the tissue vs. high numbers of short lived, quickly circulating neutrophils in the blood, for instance). The spatial organization of these cells within the body made a lot of sense to me and really helped me to grasp the particular names and functions of all these different immune cells.