Immunology is the field of science that studies the different mechanisms by which animals can discern between their own components and foreign ones, react against the foreign and memorize this for the future.

Immunology, as a scientific subject, started in the XVIII century, as a part of Microbiology. This was when the first vaccine against human smallpox appeared. Edward Jenner (1749-1923) observed that people who had suffered bovine smallpox were resistant to human small pox. These studies continued until the 19th century, when thanks to Louis Pasteur's (1822-1895) work, new technologies were developed which made possible the creation of new human and animal vaccines against different diseases . One of the first concepts defined in the development of immunology was the term "immune". It referred to those persons or animals that had survived an infection or, not having suffered it, were resistant. Two concepts then appeared: Natural Immunity and Adaptive Immunity.

Pasteur Institute , Paris.

Besides the mechanical barriers (skin, mucous secretions, low stomach pH , proteolytic enzymes, etc.) which are very  important in fighting against Antigens, mammals have other non specific mechanisms as part of Natural Immunity. Natural Immunity is the first immunological  non specific barrier of the pig for fighting against infections without any previous immunization. This response is produced in a few minutes or hours after the aggression, and is mediated by phagocytic cells, natural killer cells (NK) and interferon. When this first barrier fails, the infection is established, and the adaptive  immunity starts to develop. The  immune mechanisms related to Natural Immunity are linked with non-specific mechanisms; i.e.; they are not caused by any specific antigen.

Adaptive immunity is the result of the immune response against a foreign molecule or antigen. A specific response is generated against an external stimulus. After the seizing process and the recognition of the antigen, different mechanisms of presentation and activation of the lymphocytes will start in order to produce antibodies and cytokines.

From the first concepts up to nowadays immunology has advanced in a progressive way. The most important advances in immunology, and particularly in porcine immunology, have been achieved in the last decades. Three developments have helped to improve knowledge of the different mechanisms in the porcine species:

Adaptive immunity is induced as a response against a specific antigen, after the collaboration among phagocytic cells, T and B  lymphocytes and the production of immunoglobulins and lymphokines (IL).

1.- The development of syngeneic pigs for the histocompatibility swine system (SLA).

2.- Monoclonal antibodies.

3.- Advances in molecular biology

1. Syngeneic pigs for the porcine histocompatibility system (SLA) have allowed for better knowledge of the genetic control of the porcine immune response, as well as its relationship to the different pathogens.

2. The monoclonal antibodies allowed for the use of very specific reagents against different cells of the porcine immune system, and better understanding of their role in the immune response mechanisms.Thanks to these antibodies, we are able to know more accurately the different types and subtypes of immunoglobulins, even the porcine histocompatibility antigens (SLA)

3. Molecular biology has provided new reagents for the diagnosis of infectious diseases, as well as the development of a new generation of vaccines that have allowed the advance in the knowledge of the porcine immune response.

Diagram of the production of monoclonal antibodies. First, a mouse is inoculated with the antigen to which the MA are to be produced. After this, the spleen is removed and fused with myeloma cells in order to produce the hybridomas that will be selected according to the antibody produced.

In these ten chapters of "An Introductory Course to Swine Immunology," we will do an overview of the main components of the porcine immune system, their mechanism of action, and their most important applications.