Are rheumatoid arthritis and systemic lupus erythematosus inversely related diseases?

Although rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) have certain features in common, the literature suggests that the two diseases are inversely related to each other in at least eight major respects, viz., age of onset in relation to reproductive fertility; psychosis; kidney disease; nutritional status; and the differential effects of pregnancy, oral contraceptive use, jaundice, and penicillamine. It is suggested that associated with RA and SLE are differing blood and/or tissue levels of a common but as yet undetermined factor: deficient levels in RA, toxic levels in SLE.