Development of Non-granular Leucocytes (Lymphocytes and Monocytes) into Polyblasts (Macrophages) and Fibroblasts in Vitro. ∗

Abstract

The question whether the non-granular leucocytes of the blood of mammals are mature, specifically differentiated cells, or cells endowed with possibilities of progressive development is still subject to discussion. The prospective potencies of these elements are especially manifest in inflammation.

Maximow 1 has claimed, since 1902, that the polyblasts or mononuclear exudate cells of inflamed tissue arise in part from local fixed cells, the resting wandering cells or the histiocytes of the tissue, but for the major part represent lymphocytes and monocytes, which have migrated from the blood vessels and have undergone rapid hypertrophy in the tissue. This double origin of the polyblasts is quite natural, for a study of the embryonic histogenesis of the connective tissue and blood reveals a close relationship between the histiocytes and the non-granular leucocytes. 2 In later stages of inflammation Maximow found the further transformation of polyblasts into fibroblasts. Thus, as the polyblasts arise in part from lymphocytes, he advocated the possibility of a transformation of lymphocytes and monocytes into fibroblasts.

This idea of a progressive transformation of non-granular blood leucocytes into polyldasts and finally into fibroblasts has met strong resistance. According to the ciominant opinion the polyblasts develop from the cells of the walls of the blood vessels (endothelium, adventitial cells) The nionocytes and lymphocytes are usually considered as specifically clifferentiated elements which are unable to produce any other cell types.

The method of tissue culture has had a decisive influence on the problem under consideration. Several experimenters have shown that the non-granular blood leucocytes can transform themselves into macrophages (polyblasts) and even into “fibroblast-like” cells in vitro (Awrorow and Timofejewsky, 3 Carrel and Ebeling, 4 Maximow, 5 Lewis, 6 Fischer 7 ). However, the problem is not completely solved as yet.