The type of immunity that defends against any invader is referred to as innate; therefore, the answer is a. The major cellular mediators of innate immunity are macrophages, neutrophils, dendritic cells, NK cells, mast cells, basophils, and eosinophils.

Passive immunity is also provided through colostrum and breast milk, which contain IgA antibodies that are transferred to the gut of the infant, providing local protection against disease causing bacteria and viruses until the newborn can synthesize its own antibodies.

Activated B cells differentiate into mucosal plasma cells that synthesize and secrete dimeric IgA, and to a lesser extent, pentameric IgM. Secreted IgA is abundant in tears, saliva, breast milk, and in secretions of the gastrointestinal and respiratory tracts.

There are two examples of passive naturally acquired immunity: The placental transfer of IgG from mother to fetus during pregnancy that generally lasts 4 to 6 months after birth; and The IgA and IgG found in human colostrum and milk of babies who are nursed.

Passive immunity can occur naturally, such as when an infant receives a mother’s antibodies through the placenta or breast milk, or artificially, such as when a person receives antibodies in the form of an injection (gamma globulin injection).

Active immunity is long term (sometimes lifelong) because memory cells with antigen-binding affinity maturation are produced during the lymphocyte differentiation and proliferation that occurs during the formation of an adaptive immune response.

Individuals rely on active immunity more so than passive immunity. Active immunity is created by our own immune system when we are exposed to a potential disease-causing agent (i.e., pathogen).

The Innate vs. Adaptive Immune Response

Cellular immunity is a protective immune process that involves the activation of phagocytes, antigen-sensitized cytotoxic T cells and the release of cytokines and chemokines in response to antigen.

There are two main mechanisms of immunity within the adaptive immune system – humoral and cellular. Humoral immunity is also called antibody-mediated immunity.

The cellular immune response consists of three phases: cognitive, activation, and effector.

Cellular immunity is mediated by T lymphocytes, also called T cells. Their name refers to the organ from which they’re produced: the thymus. This type of immunity promotes the destruction of microbes residing in phagocytes, or the killing of infected cells to eliminate reservoirs of infection.

T cells are a part of the immune system that focuses on specific foreign particles. Rather than generically attack any antigens, T cells circulate until they encounter their specific antigen. As such, T cells play a critical part in immunity to foreign substances.

B cells are responsible for antibody-mediated immunity.

is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

Nickel, certain dyes, and the active ingredient of the poison ivy plant are common examples. The response takes some 24 hours to occur, and like DTH, is triggered by CD4+ T cells. The actual antigen is probably created by the binding of the chemical to proteins in the skin.

cell-mediated immunity, so named because the T cells themselves latch onto the antigens of the invader and then initiate reactions that lead to the destruction of the nonself matter. B lymphocytes, on the other hand, do not directly attack invaders.

Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria.