Guinea pig bone marrow basophilopoiesis.

Basophilopoiesis was produced in guinea pigs with daily injections of sheep blood. Bone marrow preparations from these animals and controls were studied by electron microscopy at frequent intervals during 14 days of injections. We found that the composition of normal bone marrow consisted primarily of neutrophils and their precursors, small lymphocytes, plasma cells, macrophages, red blood cell precursors, megakaryocytes, and myeloblasts. The basophil lineage and blasts of any type were seen infrequently prior to injections. Serial injections of sheep blood produced a marked, early expansion of blasts and young basophilic myelocytes, followed later by the presence of numerous mature basophils. This proliferation was accompanied by a generalized granulocytic proliferation. Megakaryocytes also increased in number and were often surrounded by basophils. An important finding in this model of basophilopoiesis was the marked early expansion of blasts which were not distinguishable morphologically from a proliferation of large lymphoid cells and lymphoblasts. These actively dividing, ribosome-filled cells underwent Golgi expansion and accumulated vesicle-containing vacuoles. Later, single and then multiple, typical, immature basophil granules appeared. The presence of these granules allowed classification of these cells as young basophilic myelocytes. The origin of immature granules from the Golgi apparatus was evident. The association of small vesicles in the cytoplasm immediately adjacent to immature granules as well as within these evolving structures suggests a role for these vesicles in the construction of new granules. These in vivo observations of granulogenesis are identical to a much accelerated process we have described in mature basophils as they rebuild granules after degranulation in an in vitro model. Moreover, the presence of multivesicular structures and vesicle-containing immature granules in granulogenesis in in vivo studies of guinea pig basophilic myelocytes has been helpful for the identification of mouse basophilic myelocytes, both in vitro and in vivo.