Anaphylactic degranulation of guinea pig basophilic leukocytes. II. Evidence for regranulation of mature basophils during recovery from degranulation in vitro.

Mature circulating granulocytes have been considered functionally end stage cells unable to reconstitute their specific cytoplasmic granules. We have reevaluated this assumption by studying guinea pig peripheral blood basophils maintained in vitro for periods up to 72 hours after anaphylactic degranulation. Guinea pig basophils degranulated in vitro by exposure to either specific antigen (sheep serum) or lectin (Concanavalin A) synthesized new cytoplasmic granules. This process was characterized by the appearance of abundant rough endoplasmic reticulum, activation of the Golgi zone, interiorization of plasma membrane, and successive formation of empty vacuoles, multivesicular bodies, immature granules, and, finally, typical mature basophil granules. Although basophil neogranulogenesis in vitro was similar in most respects to that occurring in the bone marrow, it differed significantly in that regranulating basophils retained the nuclear characteristics of mature granulocytes. New basophil granule formation was more prominent and developed earlier when sheep serum was employed as the degranulation stimulus. Cultures degranulated with Concanavalin A, and, less commonly, sheep serum, also contained small numbers of basoblasts, large bizarre basophils with immature nuclear and cytoplasmic features, cytoplasmic lipid droplets, and mature, immature, and fused granules. These cells may arise by a process analogous to lymphocytes blast transformation.