Studies on ribosomes of rat spleen during the immune response

Abstract

Microsomes and ribosomes (i.e., microsomes treated with sodium deoxycholate) have been prepared from homogenates of spleens of nonimmunized rats and rats that were immunized to sheep erythrocytes. The method used to prepare microsomes allows the release of ribosomes from endoplasmic reticulum without the aid of detergent. Particles thus obtained were sedimented by zonal centrifugation through a sucrose gradient. Six peaks of optical density of 254 mμ were observed that represented 65S, 81S, 105S, 120S, 154S, and 175S. The predominant peak was 120S. Similar optical density profiles were found with both microsomes and ribosomes from spleens of all rats, immunized and nonimmunized. Labeling in vivo with 32P of RNA associated with ribosomes from immunized rats showed that the relative specific activity increased to a maximum of about twofold at 72 hours after injection of antigen over that found in nonimmunized animals. The relative amount of amino acid incorporated in a cell-free system by microsomes or ribosomes increased with immunization. With ribosomes, this amount reached a maximal twofold at 3 days after injection of antigen; with microsomes, it was a maximal 1.3-fold at 2 days after immunization. Zonal centrifugation of incubation mixtures showed loss in the 120S region, and larger polysomes with concurrent increase in 81S with time.