Immunocompetent cells development

Whereas macrophages and lymphocytes play key roles in immune responses, their presence in the early inflammatory response is generally not considered to be an immune reaction. As will be seen later under Immune Responses, specific events in which the macrophages, lymphocytes, and plasma cells participate can lead to immune responses. Macrophages process and present antigens (foreign materials) to immunocompetent cells and thus are key mediators in the development of immune reactions. 

One may well wonder, however, whether the results represent some potential not normally realized in vivo, since under normal conditions the embryonic liver does not show demonstrable immunological capacities, nor does it normally contain significant numbers of lymphocytes. The question has particular pertinence if one wishes to determine the normal source of immunocompetent cells, since a central concept of embryology has been that development involves a series of limiting events and that early embryonic cells have many potentials which they do not realize in their normal environment. The experiments of Taylor and of Tyan and Cole cited are most readily interpreted in this manner. 

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