An ultrastructural, cytochemical and freeze-fracture study of the surface structures of Brugia malayi microfilariae.

Ultrastructural analysis of the cuticle of Brugia malayi microfilariae indicated that it is composed of 2 regions: the inner one 15-20 nm thick with a homogeneous aspect and the outer one, designated as epicuticle, which is 15-20 nm thick. Three laminae separated by electron-lucent regions were seen in the epicuticle. Labeling of the cuticle and epicuticle of B. malayi and Wuchereria bancrofti microfilariae was observed when thin sections of Lowicryl-embedded parasites were incubated in the presence of gold-labeled phospholipase-C. Replicas of freeze-fractured microfilariae showed the presence of 2 fracture planes in the epicuticle and no fracture plane in the inner region of the cuticle. The P face of the epicuticle outer fracture plane presented few particles similar to intramembranous particles (IMPs). The epicuticle inner fracture plane P and E faces presented large numbers of densely-packed small particles and many protuberances. Also, fracture faces of hypodermal and muscle cell plasma membranes were analyzed. Faces P and E of fractured membranes showed the presence of typical IMPs. P faces of both membranes showed larger amounts of particles than E faces. Fracture of muscle plasma membrane revealed a linear array of particles disposed in parallel rows on its P face.