lymphocytes , the cells competent to initiate immune responses , can be divided into two major groups : thymus-derived or t cells responsible for `` '' cellular immunity '' '' ( e.g . delayed hypersensitivity reactions ) and bursa ( or bursa-equivalent ) derived or b cells which produce immunoglobulin ( antibody ) molecules and are involved in `` '' humoral immunity '' '' .
C0021027
e immunoglobul
C0003241
( antibo