Why is lupus so different in different people?

Lupus: Lupus is a disease in which "self-reactive" autoantibodies cause damage to the body. Many different tisissues can be involved depending upon the specificity of the "self-targeted" antibody. At times, these antibodies cause collateral damage in non-specific ways as the result of "immune complexes" ( the antibody and a self-antigen) that circulate in the blood stream triggering inflammatory damage.

Lupus: Because an illness is made up of many different symptoms, and since we are all genetically different, different people with the same disease can have very different expressions of the disease.