The appearance and significance of phospholipase A2 in lymph draining tuberculin reactions

Popliteal and prefemoral lymphatics of sheep were cannulated, and lymph was collected before and during the course of responses to PPD and concanavalin A. Hyperemia-inducing activity (HIA) and phospholipase A2 (PLA2) were released into lymph in response to antigenic stimulation, whereas lymph plasma draining unstimulated lymph nodes had consistently little or no detectable HIA and PLA2 activity. HIA appeared in the lymph efferent to the stimulated node at a time when blood flow to the responding node was enhanced. While the appearance of HIA did not directly correlate with changes in lymphocyte output, lymph protein concentration, or lymph flow rates, there was, however, a statistically significant correlation between HIA and PLA2 levels in lymph plasma, suggesting that extracellular PLA2 may contribute to the vasoactivity in lymph and thereby modulate blood flow to areas of antigenic stimulation. Vasoactive lymph, injected into rabbits, induced hyperemia via an indomethacin-sensitive pathway, since the induction of hyperemia was abrogated by pretreatment of injection sites with indomethacin. The extracellular release of PLA2 in response to inflammatory stimuli may represent an amplification mechanism for the generation of high levels of prostaglandins found in lymph draining stimulated nodes.