People with lupus, the immune system mistakenly attacks the body's own natural tissues. most of the time immunosuppressives work to downregulate (suppress) this attack by interfering with the synthesis of DNA, the material in the cells that contains the blueprints for all of your genetic information!!
The cells in the heart need a constant supply of nutrients / oxygen and to get rid of their waste products ans that why it needs its own special circulatory system.