the spleen is involved differently in different ethnic groups with this disease. spleen is the organ which filters old rbcs and destroys them. old rbcs are stiff and cannot pass through some very narrow slits in the spleen. but in sickle patients all cells very quickly become stiff and thus keep clogging up the spleen. starting from a very young age segments of the spleen die because of this problem. in the pure form of this disease the whole spleen is dead and shrunken before the patient become adult. normal spleen keeps a large store of b cells which make antibodies and protect us from bacteria. loss of a working spleen leads to loss of protection from such bacteria.