GMAT Sentence Correction (SC) | Re: The cytokines of the immune system, acting as signalers to adjacent

The cytokines of the immune system, acting as signalers to adjacent cells, can provoke dangerous inflammation; the resultant autoimmune disease, characterized bycartilage and bone that become damaged although they are not actually attacked by the immune system, are known as "rheumatoid arthritis."

(A) cartilage and bone that become damaged although they are not actually attacked by the immune system,are
(B) cartilage and bone that become damaged although they are not actually attacked by the immune system, is