There are 4 different abnormal lymphocyte phenotypes: B cell positive, NK cell negative B cell negative, NK cell positive B cell negative, NK cell negative B cell positive, NK cell positive In most forms of SCID, T cells are absent (T -); the number of B cells and / or natural killer (NK) cells may be low or none (B -; NK -) or high or normal (B +; NK +), depending on the form of SCID.