THE EFFECTS OF CELL NUMBER, CONCENTRATIONS OF MITOGEN AND GLUTAMINE AND TIME OF CULTURE ON [H-3] THYMIDINE INCORPORATION INTO CERVICAL LYMPH-NODE LYMPHOCYTES STIMULATED BY CONCANAVALIN-A

The amount of [H-3]thymidine incorporated into DNA in lymphocytes stim ulated with Concanavalin-A increases exponentially with time at differ ent concentrations of glutamine, reaches a peak value, then gradually decreases. When the value (log(10) thymidine incorporation(glutamine) (present)-log(10) thymidine incorporation(glutamine) (absent)) obtaine d from the exponential phase is tion plotted against time, a linear pl ot is obtained for each glutamine concentration. When these linear rat es of incorporation are plotted against glutamine concentration, hyper bolic curves are obtained for different times of culture. The peak val ue of incorporation (which reflects the final number of cells which en tered the cell cycle) is determined by the concentration of mitogen an d occurs at an earlier time as the number of cells in culture is incre ased and as the concentration of glutamine is increased. These finding s suggest that increasing the plasma glutamine concentration above the normal physiological level may be of value in increasing the prolifer ation of lymphocytes in conditions of lymphopenia. Adenosine, a fuel o f purine nucleotide synthesis, which may affect the lymphoproliferativ e response also via specific adenosine receptors, increases the rate o f incorporation of [H-3]thymidine but this effect depends upon the con centration of glutamine; at low concentrations of glutamine, the stimu lation by adenosine is apparent whereas at high concentrations of glut amine adenosine appeared to inhibit proliferation. Our data presented in this paper suggest that not only the number of cells and the concen tration of mitogen, but also the concentration of glutamine, may play a role in determining the proliferative response of mitogenic stimulat ed peripheral lymphocytes. This emphasises that care must be taken to carry out a full kinetic study, including varying the concentration of glutamine to assess in these types of experiments whether a particula r compound or condition causes immunostimulation or immunoinhibition.