Classification of Defense Mechanisms
In pathological physiology, three main groups of barriers prevent the development of neoplasms. Each is activated at a specific stage of interaction between the body and the pathogen:
- Anticarcinogenic mechanisms — the first line of defense. Their main task is to prevent the interaction of carcinogens with the genetic apparatus. This is achieved by creating obstacles to the penetration of carcinogens into the body, inside the cell, and directly into the nucleus, as well as by preventing their action on the genome.
- Antimutational mechanisms — the second line. They aim to protect the genome and repair DNA if the carcinogen reaches its target. These include the detection and elimination of oncogenes and the suppression of their expression.
- Anticellular mechanisms — the third line. They aim to eliminate already transformed cells by detecting tumor cells, inhibiting their growth, and finally destroying them.
Anticarcinogenic Defense: Chemical Factors
This group of mechanisms performs three main functions: inhibiting or blocking the penetration of carcinogens into the cell and nucleus, preventing their action on the genome, and inactivating and eliminating carcinogenic agents. Protection against chemical carcinogens is implemented through the following pathways:
- Phagocytosis: active engulfment and subsequent destruction of chemical carcinogens by phagocytic cells.
- Immunological inactivation: chemical blastomogenic agents act as haptens. Their inactivation occurs via antibodies and T lymphocytes, ultimately leading to the destruction and elimination of agents from the body.
- Competitive receptor blockade: non-carcinogenic metabolites bind to cellular receptors, physically preventing true carcinogens from interacting with the cell.
- Metabolic inactivation: destruction of carcinogens inside cells and biological fluids, including oxidation, reduction, and demethylation processes. Physicochemical inactivation, particularly glucuronidation and sulfation, plays a crucial role.
- Elimination from the body: inactivated substances are excreted via urine, feces, saliva, bile, and sweat.
Protection Against Viruses and Radiation
The body possesses specific barriers against biological (viruses) and physical (radiation) factors.
Defense against oncogenic viruses prevents their entry and replication:
- Humoral response: plasma cells produce antibodies (Ig) in response to viral antigens. These antibodies interact with the virus, blocking its contact with membrane receptors. The primary effect is the prevention of transfection (entry of viral nucleic acid into the nucleus) and subsequent oncogenic transformation.
- Interferon (IFN) action: these specific proteins inhibit or completely block the intracellular replication of viruses.
- Nonspecific cellular cytolysis: detection and destruction of virus-infected cells carried out by NK cells, cytotoxic T lymphocytes, mononuclear phagocytes, dendritic cells, and astrocytes.
Antioxidant defense neutralizes products of radiolysis and free radical oxidation:
- Scavenging free radicals (oxygen, lipid). The enzyme superoxide dismutase (SOD) catalyzes the reaction of oxygen radicals with hydrogen ions to form hydrogen peroxide. Non-enzymatic scavengers such as tocopherols and glutathione compounds also play a role.
- Destruction of peroxides and hydroperoxides (organic and inorganic compounds, lipids, proteins). Endogenous antiperoxide agents such as catalase, glutathione peroxidase, and glutathione reductase perform this task.
Antimutational and Anticellular Mechanisms
If anticarcinogenic mechanisms fail, oncogenes are activated, leading to tumor growth. In this case, internal reserves are mobilized:
- Antimutational mechanisms: their main goal is to detect, eliminate, and/or suppress the activity of oncogenes. This defense is implemented through tumor suppressors (anti-oncogenes) and active DNA repair enzyme systems.
- Anticellular mechanisms: if a cell still undergoes mutation, the system shifts to eliminating transformed cells. These mechanisms aim to precisely detect tumor cells, inhibit their pathological growth, and completely eradicate them from the body.