RESPONSE OF FREE CELLS IN PERITONEAL CAVITY OF MOUSE AFTER INJECTION OF POLYSTYRENE PARTICLES

Young adult female mice (Charles River strain) were given a single intra-abdominal injection of 1.12×1010 Polystyrene (Latex) particles with a mean diameter of 0.796 μ, suspended in 3 ml of 0.9% saline. Animals received a single i.v. injection of thymidine-3H one hour prior to sacrifice. Free peritoneal cells were harvested by peritoneal washings at various time intervals following injection of the particle suspension. This method gives reproducible quantitative results with regard to absolute cell numbers involved in the response to this non-antigenic stimulus. Differential counts, grading of phagocytic particle loading and autoradiographic analysis were made on smear preparations of the peritoneal exudate. The phagocytic reaction comprised granulocytes and a heterogeneous population of mononuclear elements. The latter could he separated on the basis of morphological, tinctorial and kinetic characteristics into various subgroups, i.e.: monocytoid cells with kidney-shaped nuclei comparable to blood monocytes; monocytoid cells with round nuclei; lymphomonocytoid cells; large lymphoid cells; and small lymphocytes, a fraction of which showed a slight phagocytic capacity. As judged from the changes in absolute cell counts, the neutrophilic granulocytes showed the fastest entry rate, followed by small lymphocytes, then monocytoid cells with kidneyshaped nuclei and other cell types. In the period between 16 and 24 hours following stimulation the absolute number of small lymphocytes dropped significantly while during the same time interval the counts of large lymphoid cells and monocytoid cells with kidney-shaped nuclei rose more steeply. Except for small lymphocytes, cells incorporating thymidine-3H into their DNA were found among all types of mononuclears. The only significant rise of the initial labeling index up to 20% following injection of this radioactive precursor was seen in large lymphoid cells and occurred during the first 24 hours following stimulation. An abortive, non-significant rise of the initial labeling index was observed around the second day in lymphomonocytoid cells. All other mononuclear cell types exhibited initial labeling indices comparable to control values throughout the observation period. Mean particle loading per cell (grade of phagocytosis) was heaviest in monocytoid cells with round nuclei throughout the experiment. A moderate mean phagocytic grade was found in lymphomonocytoid elements and monocytoid cells with kidney-shaped nuclei. Lower phagocytic grades were seen in neutrophilic granulocytes and large lymphoid cells. The highest percentage of the total phagocytic performance (mean phagocytic grade per cell X absolute number of cells of the same type) was observed for neutrophilic granulocytes during the first 8 to 12 hours following stimulation, later for monocytoid cells with kidney-shaped nuclei. Except for small lymphocytes all types of mononuclears were engaged to a considerable extent in phagocytosis, particularly in later stages after injection of the particles. Cells showing high grades of phagocytosis usually had medium-sized nuclei. Many DNA-synthesizing cells were heavily loaded with particles indicating that proliferation may still go on while differentiation towards phagocytic capacity has already reached a high degree. The findings are discussed in relation to problems of macrophage precursors, cell emigration from the blood stream, transformation of lymphoid elements and local proliferation of mononuclear cells. © 1969 Springer-Verlag.