5.5 A lymphoid network for recognition: a summary.

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Through the immune or lymphoid system the individual communicates with its environment. The system, with cells spread through all tissues of the body, is a sense-organ with a memory attached that discriminates between self (the body's own components) and non-self (foreign matter and organisms in the environment). It defends the self and eliminates non-self substances. Throughout infancy the system learns to know and to recognize the usual antigens that occur in the environment where it grows up. The immune system works with macromolecules that are called antibodies. Antibodies are produced by lymphocytes. The lymphocytes and the freely circulating antibodies have recognition sites on their surfaces by which they can identify, and discriminate between thousands of different organic and non-organic substances that occur in nature. In the early years of childhood the immune system succeeds in cultivating a network of recognition sites that accurately represents the environment in which the individual grows up, just as the brain develops an internal image of the smellable, touchable, audible, visible world. This is made possible by Darwinian selection in a fast time-window (with a response time of days/weeks) that is even faster than the evolution of microorganisms. The shapes of antibody molecules have been selected by the antigens which the individual encounters. When a lymphocyte produces an antibody with recognition sites on it's surface that fit the antigen fairly well it's production is stimulated more than that of a lymphocyte generating a less well fitting antibody. So the best recognition sites increase in numbers and the other varieties perish and disappear from the scene. It is a Darwinian type of selection, not unlike the breeding of dogs with special properties of shape and behaviour. Selective breeding of antibodies however takes place within the individual's life time.

The immune system's molecules and cells not only recognise antigens, they also recognise each other. Since all recognised objects are called antigens, the immune-globulins have a double role, that of antigen and of antibody. As a consequence, antibody producing lymphocytes can stimulate as well as suppress other cells of their kind. By engaging in mutually suppressing and stimulating activities, the numerous varieties of individual cells and molecules constitute a network, a response-system of interacting components, an "evolving species". These oscillations are comparable to those in a "prey - predator"relationship.

When the immune network is stimulated by an antigen this elicits an increase of those lymphocytes that secrete the best fitting type of antibody for that specific antigen. There is some time-delay due to the succeeding generations of lymphocytes in the evolution of the immune response. In due time, the encounter with an antigen produces a shock-wave that travels through the system and that eventually leads to the elimination of the antigenic stimulus (by phagocytosis, agglutination and lysis or other means). After a while the shock wave (and the accompanying fever and malaise) dies down and the equilibrium of the system is reestablished. One thing has changed however: there is a permanent memory trace of the disturbance in the form of circulating lymphocytes that preserve the internal image of the encounter with the antigen. At the next contact with the antigen the response will be fast and efficient, so that only a ripple of a disturbance will pass through the network, no fever, no malaise: the individual has become immune to that particular antigen. The lymphoid system has acquired an internal image of a relevant part of the perceived world, and this we have labelled cognition.

During their early years infants have learned to cope with foreign stimulation, such as different kinds of food and various infectious agents. "Foreign" has become more or less "familiar" in the process. A flexible response system has acquired a file of substances carrying the label of self (familiar) or non-self (foreign). After a successful learning period of several years the immune system has become able to function adequately.

Like any regulatory system the lymphoid network that maintains an equilibrium between self and non-self is never completely at rest. Even during periods of relative calm the constituents of the immune system will oscillate around mean values of population density. The coupled oscillators form an internally coherent dynamic network that responds more efficiently to stimulation than if it were in static equilibrium.

With advancing age the LAD becomes prone to errors. Inaccuracies in recognising and labelling lead to attacks on innocent organs in the category of self. This is the cause of auto- immune diseases which may affect the blood-forming organs, the lining of the joints, and the white matter of the nervous system. The phenomenon of auto-immunity has its counterpart in the VAD, where semantic confusion may lead to false alarms and unjustified verbal aggression.

5.6 Concentric organisation of the NAD; rigidity and plasticity.