Quantitative serological analysis of a rabbit anti-rat lymphocyte serum and preliminary biochemical characterisation of the major antigen recognised.

Rabbit antisera to rat thoracic duct lymphocytes were examined by absorption analysis with quantitative radioimmunoassays to determine the tissue distribution of the antigens recognised and the amount of antibody against different specificities. Seven of eight sera were remarkably specific for leucocytes and one serum was analysed in detail. In this serum about 70 per cent of the antibody was leucocyte specific and most was against determinants on thymocytes, bone marrow cells, peripheral lymphocytes, and macrophages. This specificity is referred to as the leucocyte-common antigen. Smaller amounts of antibody were specific for antigens on peripheral lymphocytes but not thymocytes, and this could be subdivided into two antigens, one present on bone marrow cells and the other not. For preliminary biochemical analysis of the leucocyte-common antigen, thymocyte membrane was solubilized in deoxycholate. The homogeneity and apparent size of the antigen was determined by gel filtration and zone sedimentation on sucrose gradients. The activity behaved as a single component with the following hydrodynamic properties: sedimentation coefficient, 5.9S; partial specific volume, 0.71 ml/g; and Stokes radius, 7.5 nm. The molecular weight (including any bound deoxycholate) was calculated to be 172,000 and the frictional ratio 2.05. All activity bound to a lentil lectin affinity column and was eluted by methyl alpha-D-glucopyranoside, suggesting that the antigen is a glycoprotein.