Antigen (Ag).

The name antigen is given to any molecule able to induce an immune and epitope response, and antigenic determinant describes the smallest part of an antigen capable of inducing and being recognised by a lymphocyte clone. Every immune cell recognises an epitope. The antigens are always foreign to the organism with the single exception of phenomena of autoimmunity.

Antigen-presenting cells and phagocytes.

The job of the phagocytic cells is the capturing and processing of antigens for subsequent presentation to the helper T lymphocytes and B lymphocytes for the production of antibodies.

Autoimmunity.

In certain circumstances (trauma, surgical processes, etc), tissues which had been sequestered up to that moment (not exposed to the immune system) can be freed into the circulatory system. These tissues can act as antigens. Epitopes of infectious agents with a similar structure to that of the components themselves can also appear, or produce defects in the regulation of immune system suppressor mechanisms. In any of these cases, the immune system generates an immune response against its own structures. It produces an immune response identical to that which would be produced against a foreign antigen, at both humoral and cellular level. This phenomenon is known as autoimmunity.

B and T lymphocytes.

The lymphocytes are the cells responsible for specificity and for the memory of the immune response. The B lymphocytes, which originate in the bone marrow, are responsible for the production of antibodies. The T lymphocytes, derived from the thymus, are responsible for collaboration with the B lymphocytes for the production of antibodies, and for the mechanisms of the cell response. Chapter 2

Cell clones.

Cell clones are a group of cells which possess identical genetic characteristics, and therefore the same function.

Complement.

This system is made up of a series of seric proteins, mainly proteases stimulated in cascade and whose main biological activities are: a) Activation of macrophages (opsonization). b) Cytotoxicity of target cells which have been previously recognised by an antibody. c) Increase vascular permeability. The complement system is very important in the defence mechanisms of innate immunity and as a collaborator in certain antibody dependent cell-mediated cytotoxic reactions.

Genes.

The genes are located in the chromosomes of the cell nucleus. They are placed  in a linear way and occupy a central specific position inside the chromosome, known as locus. The genes consist of a DNA portion that codifies for a specific protein. Several genes that codify for related proteins can be in the same locus.

Fluorescence microscope.

The fluorescence microscope uses the ultraviolet range of the light spectrum for observation instead of the visible spectrum, allowing it to capture selective emissions of ultraviolet light from materials which have previously been marked with a fluorescent marker, for example, fluorescein isocyanate (FITC). The microscopes either use transmitted light (the beam comes from below the specimen) or epi-illumination (the beam comes from above the specimen).

Haplotype.

The entire series of coded alleles in each chromosome.

Lectins or Mitogens.

These are protein substances derived from plants and bacteria. They act via the carbohydrate determinants of the cell membrane of the lymphocytes resulting in a phenomenon of lymphocyte activation (lymphocyte division). The most well-known are: Phytohemaglutinin (PHA) and Concanavalin A (Con A) which stimulate the T lymphocytes, LPS (lipopolysaccharide) which stimulates the B lymphocytes and Pokeweed (PWN) which stimulates both lymphocyte populations.

Locus.

This is the position of the DNA in the chromosome, in which is found a gene or several genes which code one or more related proteins.

Monoclonal antibody (MA).

The MA were produced for the first time by Kholer and Milstein in 1975, who were awarded the Nobel Prize for Medicine in 1984 for their discovery. They managed to fuse two cells and obtain a hybrid (Hybridoma) which had functional characteristics of both cell populations. They fused a B lymphocyte from the spleen of a mouse immunized with sheep erythrocytes which produced antibodies against an erythrocyte epitope, with mouse myeloma cells that lived indefinitely "in vitro". They obtained a hybrid that was able to permanently secrete immunoglobulins against the sheep erythrocyte epitope, as the hybridoma had also acquired the capacity to secrete myeloma immunoglobulins and the ability to live "in vitro". In other words, they managed to produce antibodies "in vitro" against a single determinant of a complex antigen structure.

PCR.

"Polymerase Chain Reaction". This is an enzymatic method that enables a specific area of DNA to be selectively amplified "in vitro". The process is divided into three steps with the repetition of cycles at different temperatures. During the first step the double-stranded DNA is denatured by heat, the hydrogen bridges are broken and both strands are separated, obtaining single chain DNA. In the second step, known as annealing, two primers (oligonucleotides of between 18 and 30 nucleotides in length, whose sequence complements the ends of a defined DNA sequence that we wish to detect) are hybridized specifically with the opposing strands flanking the area of the DNA which is to be amplified. During the third step, the extension, a DNA polymerase synthetizes a strand of DNA complementary to each of the template strands, adding nucleotides to the ends of each of the hybridized primers. The newly synthesized strands serve as templates in the next cycle. The cycles are repeated between 20 and 45 times, resulting in an exponential accumulation of the amplified DNA fragment.

Porcine immunoglobulins (Ig).

The term immunoglobulins refers to all those proteins which have common and characteristic structural features, whether they have antibody activity or not. The word antibody is a functional concept used to describe the proteins which originate as a response to antigenic stimulation. Nevertheless, both concepts tend to be unified given that all antibodies are immunoglobulins and, in theory, any immunoglobulin could work as a antibody. Chapter 5.

Prevalence.

Percentage of positive animals at a given time.

Radioisotope.

This is a radioactively marked atom, used to observe and measure certain biological activity; in this case, the immunoproliferation of lymphocytes. The quantification of the radioactivity of b particles is carried out using a scintillation counter.

Scanning electron microscope.

This type of electron microscope examines the whole sample from point to point, compared to the transmission electron microscope which examines a large part of the cut sample, with a very concentrated electron beam which scans every part of the sample until it can be visualised in its entirety tridimensionally. The magnifying capacity of this microscope is around 100,000 times, compared to the 1,000,000 of the transmission electron microscope.

Seroconversion.

Comparative study of the antibody titer obtained from the same animal with an interval of approximately 21 days difference. The initial titer can be less than that of the second sample (there is seroconversion), the same (it does not seroconvert, basal response) or higher (becomes seronegative).

Tolerance.

The term tolerance describes a lack of immune response against a particular antigen or groups of antigens. Tolerance can be brought about by several factors: by sequestered antigens, or by pathological mechanisms which affect the response of B lymphocytes as well as T lymphocytes.

Xenotransplant.

Transplanting tissues or organs between two different species. In this case, the pig is being studied as a potential donor of organs to human beings.

Up

Index