We have studied the physical interaction between macrophages and lymphocytes during the immune response to purified protein derivative of tuberculin (PPD) in vitro. Mixtures of peritoneal macrophages and lymph node lymphocytes from guinea pigs immunized with tubercle bacilli formed cell clusters during 20 h of culture with PPD. The number of clusters produced was correlated to the number of immune lymphocytes in the cultures. Peritoneal macrophages which had been pulsed with PPD and untreated lymph node lymphocytes produced cell clusters in the absence of free PPD in numbers equivalent to those produced by the same cells in the presence of free PPD. In cultures containing a mixture of PPD-pulsed macrophages, not-pulsed macrophages, and immune lymphocytes with no free PPD, cell clusters developed mainly between the antigen-pulsed macrophages and lymphocytes. Cluster formation was antigen-specific with the specificity residing in the lymphocytes, mainly or exclusively in the T lymphocytes. These data indicate that in the process of cell cluster formation macrophages serve as antigen-binding (or -processing) cells, while a subpopulation of lymphocytes interact physically and specifically with the macrophages.

The specific rotation of secondary butyl alcohol was measured in dilute solutions of cyclohexane at intervals of 5° between 20°C and 70°C inclusive. After corrections for solvent effect and change of refractive index with temperature had been made there remained a definite temperature dependence of the rotivity. Interpretation of the results on the basis of three optically active rotational isomers (two of equal energy and the third less stable) gave the rotivity of the third isomer as −21° and the sum of the other two as +21°. The heat of isomerization was found to be 803 cal. per mole. The concentrations of the three rotational isomers at 20° are calculated as 42.3 percent, 42.3 percent, and 15.3 percent.