The Effect of Capping by Anti‐immunoglobulin Antibody on the Expression of Cell Surface Immunoglobulin and on Lymphocyte Activation

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Abstract
The ability of mouse spleen cells to bind anti‐mouse immunoglobulin antibody labelled with 125I (anti‐mouse Ig Ab 125I) in vitro was measured. The validity of this technique for quantifying the amount of surface immunoglobulin on mouse spleen cells was established by showing that the specific uptake of anti‐mouse Ig Ab 125I was linearly related to the number of spleen cells present. The technique was used to assess the exposed immunoglobulin determinants on mouse spleen cells after the redistribution of their surface associated immunoglobulins to a polar cap (capping) had been induced by anti‐mouse Ig Ab. It was found that after capping the amount of surface immunoglobulin recovered almost to control levels, but showed no further increase. Treatment of spleen cells with chymotrypsin and papain but not trypsin markedly reduced the quantity of surface immunoglobulin. The rate of immunoglobulin resynthesis after chymotrypsinisation was not affected by previously capping the surface immunoglobulins. Concentrations of anti‐mouse Ig Ab which induced capping of the surface immunoglobulin of spleen cells did not stimulate them to lake up (3H) thymidine although under the same culture conditions spleen cells were activated by phytohaemagglutinin and lipopolysaccharide. It is considered that capping is not in itself a sufficient stimulus to bring about in spleen cells either an increase in the density of the surface immunoglobulin or the initiation of DNA synthesis.