Antigens MCQ - Practice Questions with Answers

• An antigen is defined as an orga­nism, a molecule, or part of a molecule or substance which may be self or non-self, can evoke noticeable immune response and can bind distinctively with antibodies.
• Antigen may be a chemical substance like a protein or a polysaccharide. 
• It may be a biological entity like, Bactria, bacterial products, fungi, parasites, viruses, different microbes, or a larger para­sites.
   

MHC:

• Major histocompatibility complex (MHC) is a tightly linked cluster of genes present on chromosome 6 in humans which encodes the MHC proteins. 
•  Human MHC molecules are also called human leukocyte antigens (HLA).
• The MHC genes are organized into three classes I, II and III which express three classes of molecules Classes I, II and III, respectively.
• Class I MHC glycoproteins are expressed on the surface of about all nucleated cells. Class I MHC molecules present the peptide antigens to T_c cells.
• Class II MHC are expressed on the surface of antigen-presenting cells and presents the antigen to T_H cells.
• Class III MHC participates in the classical pathway and in the alternate pathway of the immune responses.

Antigen Presenting Cells (APCs):

• An antigen-presenting cell (APC) is an immune cell that detects, engulfs, and informs the adaptive immune response about an infection. 
• Dendritic cells are immune cells that process antigen material; they are present in the skin (Langerhans cells) and the lining of the nose, lungs, stomach, and intestines. 
• Macrophages also function as APCs. 
• Before activation and differentiation, B cells can also function as APCs.