Chapter 10

I am going to blog on Ch 10 this week

1. Chapter 10 is concerned with "over-reactions of the immune system", more commonly known as "allergic reactions". These reactions fall into 4 hypersensitivity groups: Type I which generally occurs through inhalation of antigen and its binding to IgE bound to its Fc receptor, particularly mast cells, which degranulate and release inflammatory mediators; Type 2 is caused by small molecules which bond covalently to components of the human cell surface and provoke B cell IgG antibody response; Type 3 occurs when soluble protein antigens bind to IgG specific to them causes inflammation; and Type 4 which involves antigen T-cell interaction and inflammatory response. The chapter spends the majority of its time going in depth into type 1 hypersensitivity reactions, so I will summarize this section: the first time a subject encounters an antigen, if the subject makes IgE antibodies for it, that antigen will become an allergic response. IgE antibodies have the highest affinity possible for an antibody and an Fc receptor, and the interaction is considered irreversible, thus the IgE antibodies act as "receptors" for mast cells, basophils and eosinophils which, once they encounter antigen again, will react very quickly and dramatically, releasing their granules and causing an allergic reaction, a reaction believed to have evolved to combat parasites.

2. Concerning the Type 1 allergic reaction, it is a bit unclear to me why it may arise in some people but not others. For this reaction to take place, a person must be exposed to an antigen, the antigen must be taken up by professional antigen presenters like dendritic cells, a Th2 Cell must then recognize the antigen and recruit a B cell to make IgE specific to that antigen. It seems this chain of events is unlikely to all occur for a small amount of harmless antigen but apparently it does and this then is an allergy. My question, though, is why this doesn't eventually happen to everyone. It seems like if we are repeatedly exposed to items such as peanuts, say, this chain of events would eventually happen to everyone--we would all become allergic to peanuts! Why doesn't this happen?

3. I am mainly baffled at the existence of these cell types (mast cells, basophils, eosinophils). I had always wondered what exactly these cells particular functions are, and I continue to wonder! It seems they exist as a sort of historical tool which may have once been helpful against parasitic infections and are now more trouble then they're worth (at least in many populations where exposure to parasites is quite low). Is there perhaps some way to inhibit IgE formation? It seems this antibody is of no use outside of provoking allergic reactions, and if we were to architect a method for stopping its production we could effectively strip these useless cell types of their receptors, rendering them harmless--perhaps an IL-4 inhibitor?