Answer:
The correct sequence is:III) Antigenic determinants from pathogen bind to antigen receptors on lymphocytes.
IV) Lymphocytes specific to antigenic determinants from pathogen become numerous.
II) Lymphocytes secrete antibodies.
I) Pathogen is destroyed.
V) Only memory cells remain.
Explanation:
Effective resistance against infection is essential for the development and functioning of the mammalian organism, and for it to be effective, multiple defense systems must be available. In order to meet these objectives, the body has developed a complex system of overlapping and interrelated defense mechanisms, which together can destroy or control almost all invaders.III) Antigenic determinants from pathogen bind to antigen receptors on lymphocytes. It consists of the binding of the foreign antigen to the specific receptors existing on the membrane of mature lymphocytes. The B lymphocytes that mediate humoral immunity express antibody molecules on their surface, which bind to foreign proteins, polysaccharides or lipids in their soluble form; T lymphocytes, responsible for cellular immunity, express so-called T cell receptors (TCR), which recognize small sequences of antigenic peptides.
IV) Lymphocytes specific to antigenic determinants from pathogen become numerous.II) Lymphocytes secrete antibodies.
Activation phase: sequence of events that occur in lymphocytes as a result of specific antigen recognition. All lymphocytes undergo two fundamental changes: a) proliferation: expansion of antigen-specific clones and amplification of the protective response, in which the CD4 T lymphocyte, capable of activating CD8 B and T lymphocytes, assumes a preponderant role; b) differentiation: stage in which effector cells and memory cells are formed. The first produce various substances that can interact with the antigen, such as antibodies and lymphokines; the second are partially differentiated lymphocytes, that is, they do not become effector cells.
I) Pathogen is destroyed.
In this phase, the T lymphocytes differentiated into effector cells migrate to the sites of attack, where they carry out their functions of eliminating pathogens, while the B lymphocytes perform them in the peripheral organs themselves.
V) Only memory cells remain.
One of the most important consequences of the adaptive immune response is the establishment of the state of immunological memory, which lies in the ability of the immune system to respond more quickly and efficiently to microorganisms that have previously infected the host and it reflects the preexistence of a clonally expanded population of antigen-specific lymphocytes. We call, therefore, the immune response that the organism gives when it comes into contact for the first time with a foreign agent and from which a series of events derives that include nonspecific innate defense mechanisms and adaptive response mechanisms, if the pathogen manages to survive the first ones.
