PAMPs bind to Pattern-recognition receptors (PRRs) on defense cells to trigger the production of inflammatory cytokines. The body activates innate immunity by recognizing molecules unique to microorganisms that are not associated with human cells called pathogen-associated molecular patterns or PAMPs.The Gram-positive cell wall activates both the body's innate immune defenses and its adaptive immune defenses.Surface proteins embedded in the cell wall can function as adhesins, secretion systems, and enzymes.Teichoic acids and lipoteichoic acids are interwoven through the peptidoglycan layers.Peptidoglycan prevents osmotic lysis in the hypotonic environment in which most bacteria live.The Gram-positive cell wall consists of many interconnected layers of peptidoglycan and lacks an outer membrane.Because of the nature of their cell wall, Gram-positive bacteria stain purple after Gram staining.There are two major branches of the adaptive immune responses: humoral immunity and cell-mediated immunity. The receptor on a T-lymphocyte is called a T-cell receptor (TCR). The epitope receptor on the surface of a B-lymphocyte is called a B-cell receptor and is actually an antibody molecule. The body recognizes an antigen as foreign when epitopes of that antigen bind to B-lymphocytes and T-lymphocytes by means of epitope-specific receptor molecules having a shape complementary to that of the epitope. A single microorganism has many hundreds of different shaped epitopes that our lymphocytes can recognize as foreign and mount an adaptive immune response against. An epitope is typically a group of 5-15 amino acids with a unique shape that makes up a portion of a protein antigen, or 3-4 sugar residues branching off of a polysaccharide antigen. The actual portions or fragments of an antigen that react with antibodies and with receptors on B-lymphocytes and T-lymphocytes are called epitopes. We recognize those molecular shapes as foreign or different from our body's molecular shapes because they fit specific antigen receptors on our B-lymphocytes and T-lymphocytes, the cells that carry out adaptive immunity. An antigen is defined as a molecular shape that reacts with antibody molecules and with antigen receptors on lymphocytes. Proteins and polysaccharides associated with the Gram-positive cell wall function as antigens and initiate adaptive immunity.
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