IMMUNOLOGY

Detailed explanation-1: -Step 1: A macrophage engulfs the pathogen. Step 2: The macrophage then digests the bacterium and presents the pathogen’s antigens. Step 3: A T helper cell binds to the macrophage and becomes an activated T helper cell. Step 4: The activated T helper cell binds to a B cell in order to activate the B cell.

Detailed explanation-2: -The humoral immune response occurs in several stages: B cell development, acquired antigen specificity, differentiation, and antibody production.

Detailed explanation-3: -The adaptive immune response in B cells, Helper T cells and Cytotoxic T cells involved four phases: encounter, activation, attack, and memory.

Detailed explanation-4: -IgM is the first antibody secreted by the adaptive immune system in response to a foreign antigen. Monomeric IgM is a heterotetramer of approximately 180 kDa. However, the secreted form of IgM exists predominantly in a pentameric configuration with a molecular weight greater than 900 kDa.

Detailed explanation-5: -The first set of responses constitutes the innate immune response. Because the recognition molecules used by the innate system are expressed broadly on a large number of cells, this system is poised to act rapidly after an invading pathogen or toxin is encountered and thus constitutes the initial host response.

Detailed explanation-6: -The immune system response to a virus. (1) Virus bearing an antigenic epitope. (2) Processing of antigen to fragments. (3) Presentation of antigen (Ag) to T cells (on the infected cell surface) and B cells (free antigenic pieces or viruses).