t cell proliferation activity 2 0 u00d7 10 7 units mg which was identical to that of a control rhull 4 sample that had not been crystallized when subjected to sds page the electrophoretic migration of the redissolved rhull 4 crystals was identical to that of the control sample similarly the reversed phase hplc elution pattern of the redissolved crystals was indistinguishable from the elution pattern of the control sample no protein degradation was apparent as a result of the long period of incubation at 22 u00b0 c more importantly the process of crystallization followed by redissolution in physiological buffer failed to inactivate the t cell proliferation activity of rhull 4 x ray diffraction data were initially collected to 2 7 u00e5 resolution using the area detector oscillation frames covered 0 25 and were measured for 10 minutes indexing and integration of intensity data were carried out using the xengen processing programs howard et al j appl crystallogr 20 383 1987 the data indexed in the tetragonal system with a 92 1 2 b 92 1 7 and c 46 5 1 u00e5 the space group is either p 4 2 1 2 or p4 3 2 1 2 subsequent x ray precession photographs of interleukin 4 confirmed the space group and unit cell parameters the tetragonal crystals are stable to x rays and diffract at room temperature for at least five days and diffract to at least 2 7 u00e5 resolution large scale crystallization can be accomplished by methods equivalent to vapor diffusion namely dialysis and ultrafiltration.