Antibody (Ig) Structure and Function

Immunoglobulin Structure and Function

• The molecular weight of the Fab portion of the Ig is not specified in the text, but it can be mentioned that Fab is the antigen-binding fragment of an antibody.
• The Fc portion of immunoglobulins provides the main characteristic feature of activating the complement system and binding to Fc receptors.

Immunoglobulin Types

• IgM has the heaviest molecular weight according to Svedberg's unit.
• The basis for classifying Ig into different types is based on the amino acid sequence of the heavy chain constant region, which determines the class (e.g., IgM, IgG, IgA, etc.).

Antibody Function

• The paratope is the region in the Fab portion of the antibody that recognizes and binds to the specific epitope of the antigen, providing the primary function of recognizing and binding to specific antigens.

Immunoglobulin Structure

• The four polypeptide chains in an Ig molecule are held together by disulfide bonds and non-covalent interactions.
• Each Ig molecule consists of two heavy chains and two light chains, with two types of light chains (κ or λ) that can be present on both arms.
• The main source of synthesis for γ-globulin is plasma cells.

Passive Immunity and IgA Synthesis

• IgG provides passive immunity to newborns.
• The main source of synthesis for IgA antibodies is mucosal tissues, such as those found in the gut and respiratory tract.

Laboratory Diagnosis

• The main focus of the laboratory diagnosis of PUO (pyrexia of unknown origin) is not specified in the text.
• Shigella bacteria are the causative agents of bacillary dysentery.
• The etiology of syphilis is not specified in the text, but it is caused by the bacterium Treponema pallidum.
• Erythroblastosis fetalis is a hemolytic disease of the newborn, caused by maternal-fetal incompatibility of the Rh blood group.