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THE IMMUNE SYSTEM
The immune system (le systeme immunitaire/il sistema immunitario/el sistema inmunologico) [E1], [E2], [E3], [E4], [E5], [E6], [ES1] [ES2] [F1], [F2] [I1] [I2] [I3]comprises a network of cells, tissues and organs that work together to protect the body. It is characterized by a high degree of diversity and complexity and represents the body's defence against infectious organisms and other pathogens: all tissues are continuously exposed to the risk of invasion by micro-organisms, such as bacteria, viruses, protozoa, fungi and parasites, that can penetrate through the skin or the mucosal membranes and cause disease. Every micro-organism that enters the body contains a wide range of different molecules (peptides, proteins, polysaccharides) that are recognized as foreign substances (called antigens/antigene/antígeno [E] [F] [I] [ES]). When an antigen is detected, the immune system responds by a series of steps (immune response/réponse immunitaire/respuesta inmune) that requires the finely regulated interaction of many different components.
Mammals have developed three main lines of defence against pathogens:
1. surface protection mechanisms, that includes non-specific physical and chemical barriers;
2. innate immunity which is a type of non-specific defence, unable to discriminate among different micro-organisms and to be potentiated by recurring contacts;
3. adaptive (or acquired) immunity, which consists of antibody-mediated and cell-mediated immune responses, stimulated by exposures to foreign substances, and is highly specific.
Non-specific responses block the entry and spread of disease-causing agents, while specific responses are tailored to an individual threat.
The immune system is associated with problems in transplants and blood transfusions, and disorders resulting from over-reaction (autoimmunity/auto-immunitŕ/autoinmunidad, allergies/allergie/alergias) and under-reaction (SIDA/AIDS/SIDA).
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