ULTRASTRUCTURAL-STUDY OF THE ENCAPSULATION RESPONSE OF THE AMERICAN COCKROACH, PERIPLANETA-AMERICANA

Pieces of altered allogeneic nerve cords implanted into the body cavity of the American cockroach are rapidly encapsulated by blood cells. The initial cellular response is the lysis of granulocytes on and near the surface of the implant. The discharged cellular components, together with an amorphous, clot-like substance, form a layer of debris which coats the foreign surface. Numerous hemocytes attracted to the reaction sites envelope the implant, forming a multilayered capsule composed of 3 morphologically distinct regions. Plasmatocytes and granulocytes participate in the cellular immune response, but granulocytes are much more reactive and form most of the structural elements of the capsule. Melanin is not a major component of the capsule as it is in capsules formed around parasites. Some of the intracellular degradative processes which precede lytic activity include autophagy, degranulation and the development of numerous microvesicles. The early reacting cells may release substances which both are chemotactic for hemocytes and serve to bind the cells together to form the capsule. Since some granulocytes are more labile than others there may be subpopulations of these cells with different surface recognition sites.