How does this happen?

The pathophysiology of Lupus as stated in previous posts is an autoimmune disease. Studies suggest that heredity plays an important role in the development of this disease. Many biochemical studies have shown abnormalities in T and B cell function, programmed cell death or apoptosis, immune complex clearance, complement function and deficiencies, and nucleosome processing.  With these problems in the immune system they lead to the abnormal functioning and thus the host’s immune system does not recognize itself and therefore attacks its own healthy cells. It still is not clear exactly what starts the immune dysregulation, but it does appear to require a genetically susceptible host affected by either a exogenous trigger meaning a trigger that is outside the body or an endogenous metabolic disturbance meaning a disturbance that comes from within the body that causes the loss of tolerance to self-antigen.

Ultimately the body attacks itself, but how? The immune complex which is when an antibody binds to an antigen once this happens then the immune complex is subject to any number of responses. In this disease the immune complex deposits in various organs, which trigger chemical mediators that cause inflammation and injury. A host with Lupus has antibodies that are going to be directed in the nuclear self-antigen including different parts of DNA, histones, proteins, and ribosomes. Specifically this disease targets double-stranded DNA so when looking to diagnose this disease looking for these specific autoantibodies. There are antibodies called anti-Ro and anti-La which are suspected to play a role in the system of photosensitivity, skin rashes, and response to ultraviolet light. Antiphospholipid antibodies which attack the phospholipids of the cell membrane may be the cause of why some patients develop blood clots that cause stroke and heart attacks.

Lupus is a disease that has a lot of unknowns about why autoantibodies target perfectly normal cells and why the disease manifests in the first place, but there is a lot of research being done to figure out this disease and to help those that suffer from it. 

This is a quick diagram to help understand how lupus attacks the body

References: 

https://www.google.com/search?q=pathophysiology+of+lupus&espv

http://www.clevelandclinicmeded.com/

http://www.britannica.com/