The macrophages essentially act as a mobile police force travelling throughout your body and tries to envelop all abnormal bacteria and other invaders. Once inside the macrophage the invading organism is imprisoned in its own space within the cell. The cell then injects chemicals that it produces into the area with the invader destroying it, if everything is going according to plan.

The invader once destroyed is then broken down into its constituent pieces and these pieces are presented like trophies on the surface of the cell so that any passing cell can see them. This only becomes important if a passing B cell or T cell happens to notice the trophy. In which case the B cell and T cell communicate with the macrophage examine the trophy and if it is deemed to have arisen from a foreign organism then the B cell designs a perfect weapon to kill it in future called an antibody. If the B and T cells confer and the trophy is thought to have been derived from the self then they USUALLY dont bother to form antibodies.

In lupus there is a defect of one or several of the above processes which are in fact far more complex than outlined. The end result is the B cell is unable to identify self from invader and decides to produce antibodies against anything a macrophage happens to be carrying.

Hence the disease can affect any tissue of the body as macrophages are present within all tissues. When this sequence of events targets the kidney the antibodies produced create an inflammatory reaction at the target site within the specific structure targeted within the kidney.

One of the first signs of this when you go to get your check up is increased protein in the urine. This occurs because the inflammatory reaction affecting the kidneys damage a very important part of the kidney filter that usually produces urine called the “basement membrane” this allows leakage of substances out of the blood where they should have remained. If damage is bad enough blood will also leak through. If You have a significant amount of blood and protein in the urine then you will have what is called glomerulonephritis, which basically means inflammation of the kidney structure known as the glomerulus. The glomerulus being the important filter that starts the process of urine formation.

When this inflammation occurs in patients with lupus it could very well be called lupus glomerulonephritis, instead it is shortened to Lupus nephritis. The severity of the inflammation determines the severity of the nephritis. And as with all things where scientists are involved they have described subsets.

CLASS I disease is mild.
CLASS II disease is also mild.
CLASS III disease can be moderately severe
CLASS IV disease is usually considered the most severe
CLASS V disease may be considered less than class IV in severity but is generally treated the same way.
CLASS VI disease generally represents scarring of the kidney or old inflammation.