IDENTIFICATION OF A PHOSPHOPEPTIDE IN BOVINE ALPHA(S1)-CASEIN DIGEST AS A FACTOR INFLUENCING PROLIFERATION AND IMMUNOGLOBULIN PRODUCTION INLYMPHOCYTE-CULTURES

Digestion of bovine alpha(s1)-casein with bovine trypsin produced pept ide(s) with an inhibitory effect on concanavalin A-induced proliferati on of mouse spleen cells. One of these peptides was isolated from the alpha(s1)-casein digest following ultrafiltration, hydroxyapatite chro matography and reversed-phase HPLC, and amino acid composition and seq uence analyses showed it to be sequence 59-79 from the phosphoserine-r ich region of alpha(s1)-casein. The isolated peptide significantly inh ibited the concanavalin a-induced proliferation of mouse spleen cells and rabbit Peyer's patch cells, whereas it enhanced the lipopolysaccha ride- and phytohaemagglutinin-induced proliferation of both cells. The peptide displayed mitogenic activity in the cell cultures without the commercial mitogen; and significantly enhanced immunoglobulin product ion. Moreover, residues 1-25 from the phosphoserine-rich region of bov ine beta-casein had a similar effect on the proliferation of mouse spl een cells and rabbit Peyer's patch cells stimulated or not stimulated by the commercial mitogen. These results indicate that caseinophosphop eptides may act as a humoral immunostimulator in cell cultures.