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interactions between cells. The group of ad-hesive molecules include for example ICAM-1 (CD54 – intercellular adhesion molecule-1), ICAM-2 (CD102), VCAM-1 (CD106 – vas-cular cell adhesion molecule) and PECAM-1 (CD31 – platelet-endothelial cell adhesion molecule). Besides the discriminative mole-cules, the receptor for polymeric immuno-globulins (p-IgR) and platelet-derived growth factor receptor also possess a regulatory func-tion.

Immunoglobulins (Ig) These are glyco-proteins of animal origin and include all anti-bodies. Their molecules consist of two identi-cal light chains and two identical heavy poly-peptide chains interconnected by disulphide bonds. The chains are spatially organised into domains (immunoglobulin domains) and modules. The first domains of the light and heavy chains are variable, while the others are constant. In the variable domains, the se-quence of amino acids of the polypeptide chains changes amongst the antibody mole-cules with diverse specificity, while in the constant domains remains unchanged. The sections of variable domains with particularly intensive changes of amino acids in individu-al positions are called hypervariable sections. The hypervariable sections of light and heavy chains are positioned in the Ig molecule side by side and form the antibody binding site, accounting for antibody-mediated specificity. There are two types of light chains (Kappa and Lambda). Heavy chain immunoglobulins are classified into five classes (IgA, IgD, IgE, IgG and IgM).

Immunoglobulins – chains Polypeptide chains constituting the immunoglobulin molecule. Each of the molecules contains at least two identical light (L) chains and two identical heavy (H) chains: There are two types of light chain: kappa (κ) or lambda (λ); they determine the type of immunoglobulin molecule (K or L). The heavy chains belong to five different isotypes: gamma (γ), mu (μ), alpha (α), delta (δ) and epsilon (ε); each of them determines membership to a specific immunoglobulin class. In addition to these

two types of chains, the molecule of polymer-ic immunoglobulins (IgM and secretory IgA) also contains one joining (J) chain and the secretory IgA molecule a secretory compo-nent (SC).

Immunoglobulins – classes Isotypic variants that differ from one another by the antigenic structure of constant domains of the heavy chains of their molecules (immu-noglobulins, chains). There are five known classes of immunoglobulins: IgG (having the heavy chain (γ), IgM (μ), IgA (α), IgD (δ) and IgE (ε)).

Immunoglobulins – effector functions All functions except those serving at the binding site. These include the ability to acti-vate the complement, bind to the cellular Fc-receptors, pass through the placenta, etc.

Immunoglobulins – genetics → see Ge-netics of immunoglobulins.

Immunoglobulins – hypervariable re-gions This is the section of polypeptide chains in the variable domains where indi-vidual amino acids are able to a greater extent to change positions, and thus allow immense diversity to generate millions of antigen-spe-cific antibodies. There are six such sections in general – three on the light chain and three on the heavy chain. During the final stereo-metric arrangement of the immunoglobulin molecule, they become mutually close and form an antibody binding site. The hyper-variable sections are also called complemen-tary determining regions (CDR).

Immunoglobulins – idiotypes Immu-noglobulin variants determined by a set of antigenic determinants, mainly in the hyper-variable sections of both light and heavy chains. Such an idiotype represents the anti-genicity of the antibody binding site. Some idiotypes can be found only in the organism of a certain individual (private idiotypes), while other can be confirmed in multiple in-dividuals (common or cross-reacting idio-types).

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