Immunologic Implications and Evasive Strategies Developed by Neoplasic Growths - Essay Example

The theory of immunosurveillance has two distinct approaches. The first approach (immunosurveillance) postulates that the immune system, as in response to other antagonistic entities that may enter any organism, develops a protective system against such entities. The second approach (immunostimulation) postulates that the immune system itself promotes neoplastic growths because the neoplastic cells themselves develop a very powerful immune system that tends to recognise the invaded organism’s own cells as hostile (Ichim, 2005). There is a third element in the research for investigating interactions between the immune system and neoplasia. This is that neoplasia deliberately develop certain defence mechanisms against the incumbent system in such a manner that they successfully evade punitive action (Chernock et al, Undated). This paper’s purpose is to investigate what these evasive strategies may be and how they assist neoplasia to evade immune reaction.
Immunosurveillance Theory
In the 1950s Lewis Thomas and Sir MacFarlane Burnet postulated the theory positing that effector cells of the immune system constantly patrol the body to actively identify and eradicate incipient tumour cells (Ichim, 2005). In 1970, subsequent research found that T-cells may be implicated in this defensive mechanism (Ichim, 2005). This theory fell out of favour in the 1980s as research studies noted certain discrepancies in it but, in the 1990s, it was again revived because subsequent research studies noted that it was partially viable (Bhardwaj, 2007). It is observed that both the innate immune system – phagocytes, NK cells, NKT cells, cytokines, proteins, etc. – and the adaptive immune system - B- and T-cells, etc. – do fight neoplasia but, ultimately, it is observed for most spontaneous tumours that the overall immune system fails to entirely rid the organism of the cancerous cells. This is so as per three acknowledged phases to the immune response – 1) the elimination phase during which nascent tumourous cells are eliminated by the immune system; 2) the equilibrium phase when the tumour cells persist but are held in abeyance by the immune system; and 3) the escape phase when the tumour cells develop strategies to combat the immune system (Bhardwaj, 2007). This is the whole concept of ‘immunoediting’ and the last phase – the escape phase – is the one the paper is interested in because it is the one in which the neoplasia develop successful strategies in evading immune reaction.
Evasive Strategies
The evasive strategies adopted by neoplasia may be pre-existing or adaptive. Since such develop from healthy normal cells, some of the progenitor cells’ evasive strategies pre-exist in them (Chernock et al, Undated).
Pre-existing Strategies: Normal cells are incorporated by certain mechanisms that assist them in evading the body’s own immune reactions. Such mechanisms may be self-tolerance, shielding from proper surveillance, antigen shedding, lymphocyte killing, secretion of immunosuppressive cytokines, lack of MHC2 expression, lack of co-stimulatory molecules and local secretion of prostaglandins and neuropeptides. These strategies are often sustained in neoplasm (Chernock et al, Undated). They ultimately, to a large extent, help the mutant cells maintain themselves with impunity in the organism’s body.
Adaptive Strategies: Nevertheless, such mutant cells are altered and have certain distinct proteins that differ from normal cells and these may be recognised by the immune system. To evade this eventuality such cells develop strategies that are not inherited from normal cells but are variants developed customarily by the mutant cells themselves as per requirements. Such adapted strategies may be up-regulation of the evasive tactics of healthy cells still existing in the mutants, down-regulation of MHC1 expression or peptide presentation, antigen modulation and strategies to inhibit lymphocyte homing (Chernock et al, Undated). These strategies are self-explanatory and are thus not expanded upon in greater detail. Instead, the paper moves on to include certain other characteristics of mutant cells that allow them to evade the immune system with impunity.

The Immunostimulation Theory
Richard Prehn (1972) formulated this theory and postulated that while transplanted tumours generate strong immune responses from the organism spontaneous tumours generate weak responses that are more stimulating to such neoplastic growth than inhibitory. Prehn’s principal hypothesis is that tumours induced by very low concentrations of the inducer, or those arising without obvious causes where the obviousness may be detectable by the immune system, tend to have very low immunogenicity that remains undetectable by the immune system and, thus, no appropriate response is arranged. Such tumours, subsequently, in the absence of a definite immune response advance indefinitely (Prehn, 2005).