EXPERIMENTAL MODULATION OF THE REACTIVITY OF PLEURAL MILKY SPOTS (KAMPMEIERS FOCI) BY FREUNDS ADJUVANTS, BETAMETHASONE AND MYCOBACTERIAL INFECTION

We studied the response of milky spots in the parietal pleura of the r at and mouse to intrapleural instillation of immunomodulatory agents s uch as complete or incomplete Freund's adjuvants and betamethasone, an d also to infection by mycobacteria (M. avium). Both incomplete (miner al oil) and complete (mineral oil plus dead mycobacteria) adjuvants, a s well as M. avium infection, induced a striking increase in the size and cellularity of the pleural milky spots whereas betamethasone cause d a slight atrophy. The extensive inflammatory infiltrates observed af ter adjuvant injection differed between milky spots reactive to comple te and incomplete Freund's adjuvants. Fifteen days after adjuvant admi nistration, the pleural milky spots of rats were still enlarged and hy percellular but differences were noted in the size of milky spots of t he pleura between the 2 adjuvant treatments: animals submitted to inje ction of complete Freund's adjuvant showed an increase in the size of milky spots from d 3 to d 15, while the size of milky spots of the inc omplete Freund's adjuvant treated group showed a decrease in size from d 3 to d 15. The milky spots at d 15 were well organised: reticulin f ibres permeated the whole area of the milky spot and the different cel l types were evenly distributed. Histiocytes, which were previously co nfined to the inner layer, were now the main cell type in all areas of milky spots. A moderate number of mast cells and a few eosinophils we re also seen. Complete Freund's adjuvant caused the formation of granu lomas in the milky spots, a change that was not detected in animals tr eated with incomplete adjuvant. The enlarged pleural milky spots that were found in M. avium-infected mice showed mononuclear cells that con tained numerous mycobacteria revealed by staining with the Ziehl-Neels en method. Our data indicate that milky spots are areas of the parieta l pleura with an elective role in the mounting of local inflammatory a nd immunological reactions of the pleural space. Milky spots may there fore be considered as important defence structures of the pleural memb ranes, reacting in accordance with the nature of the stimuli reaching the pleural space.