The biological recognition of foreign from native particles as a problem in surface chemistry

Abstract

There is a large area of cellular interactions in biological systems which has not been thoroughly explored from a physical chemiCal point of view. One reason for this is the inherent difficulty of the systems (from both a biological and physical chemical point of view), but another reason is without question that in several vital areas of biological interest the colloid and surface chemist is not aware of the problems which in the author's opinion would be well served by a closer inspection by the colloid scientist (1). I t is the intention in this paper to point out both the biological and surface chemical problems involved in the by the body of non-native particles, such as bacteria, which somehow enter the blood stream. Foreign particles entering the mammalian blood stream are usually removed in a matter of minutes. They are removed from the blood stream by cells located largely in the liver and spleen which are capable of recognizing these foreign particles and cause them to enter the cell by the process of phagocytosis. It is important to recognize that these are in fact two distinct processes (2): firstly, recognition, which in the present context may be regarded as a sticky collision, and secondly, the actual process of engulfment. The subsequent fate depends upon the balance of the powers of the enzyme system of the cell to destroy the particles and ultimately to initiate antibody formation, and the power of the bacteri~ to resist the enzymes, multiply, and attack the host. The powers of the in the mammalian system are extremely acute; for example, native red blood cells have a lifetime in man of the order of 100 days. At the end of this time they are recognized as different and removed. Only recently (3) has this been attributed to a measurable change in the chemical composition of the red cell. It should further be remembered that any foreign particles will normally be diluted by other particles, i.e., red cells and white cells, by several orders of magnitude. This paper will consider only the first or recognition part of the problem, but since it is of considerable interest to surface chemists the second process will be here mentioned briefly. Tait (4), Ferm (5), and Ponder (6) discussed at length the process of engulfment in terms of interfacial tensions. Unfortunately their hypotheses were difficult to test and have largely been ignored, although it has been pointed out by Pethica (7) that it is questionable whether surface tension can be interpreted in the manner proposed by these workers. Some work on the effect of detergents on the process of phagocytosis has been reported (8, 9), but in view of the interactions of detergents with proteins and their lyric action, it is difficult to interpret. Further, it treats the process of phagocytosis as a whole and does not allow us to consider recognition and engulfment separately. This of course raises the point, which must always be kept in mind, that the processes are separated only for convenience and that we are deMing with a living system. The metabolic processes involved in phagocytosis have been studied by Karnovsky (10) and others and well illustrate the preceding point. The problem of can be and