Cross-reaction of albumin with polyclonal LH antibody on western blots

When pituitary tissue was subjected to Western blot analysis utilizing polyclonal antibody NIDDK-rLH-S-10, bands at 17 and 19 Kd representing LH subunits were identified. In addition, a high molecular weight 66 Kd band was seen. Surprisingly this high molecular weight band was also seen in rat cerebral cortex, brain stem, hypothalamus, spinal cord, lung, liver, pancreas, spleen, kidney, testis, and serum. Antibody preabsorbed with iodination grade rat LH antigen no longer recognized the 17 and 19 Kd bands in pituitary, but recognized the 66 Kd bands in pituitary and the other tissues examined. Since 66 Kd is the molecular weight of albumin, we found that antisera to rat albumin recognized this same high molecular weight band in the tissues examined. Preabsorption of LH antibody with albumin reduced the ability of that antibody to recognize this 66 Kd. A monoclonal antibody to bovine LH beta-subunit recognized only the LH protein in anterior pituitary, but no high molecular weight band in either pituitary or the other tissues studied. Finally, 10, 100, and 1000 micrograms of rat albumin caused no substantial interference under conditions of RIA. We conclude that the polyclonal antibody, provided by the NIH, is excellent for conditions of RIA, but caution must be exercised when it is used for Western analysis where some lots of this antibody may recognize other unrelated proteins.