Natural Immunity and Macrophages Introductory Remarks
15 years ago macrophage sessions, usually placed at the end of an immunology meeting, were apparently devoid of any interest to a real immunologist and were therefore at most occasions nearly empty except from the speakers and some discussants. In the meantime this picture has completely changed and “macrophages” have not only a full audience, but, as today, are happy to be put at the beginning of the meeting. What are the reasons for this development? If one looks at the contributions of today and takes also into account facts, which are not discussed today, one realizes that macrophages have successfully squeezed into most branches of immunological reactions. Although they have kept their nonspecific properties, they influence by various means specific immunological reactions. Some of the many secretory products of macrophages seem to be of high relevance for regulatory processes like I1-1 or prostaglandins. More directly macrophages influence immune reactions by presenting antigen associated to cell-membrane structures like Ia antigens. Whether or not this property is unique to macrophages or whether it is in fact also or exclusively a property of dendritic cells is still a matter of debate as well as the question, whether the dendritic cell is a cell type quite distinct from macrophages or whether these two cell types are related.