During a parasitic infection, which of the following would most likely be responsible for phagocytosis of organisms and the release of histamine, respectively?

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11ecba2d_0fd6_2654_a3bf_ebab2092aed9_MD0008_00 A number of cells and proteins are directly involved in protecting the body against foreign pathogens such as parasites. These cells and proteins, along with the skin and mucous membranes, constitute the innate immune system. The innate immune system activates relatively quickly (minutes to hours) and is said to work in a nonspecific manner because of its ability to target a variety of pathogens for destruction. The cells that make up the innate immune system include macrophages, dendritic cells, natural killer cells, and basophils. The primary function of macrophages, which can either travel the body or remain fixed in a specific tissue, is to degrade pathogens and dead body cells. The degradative function of macrophages is performed via phagocytosis, the process of engulfing solid particles (eg, parasites) designated for destruction into phagocytic vesicles called phagosomes. Within the cell, phagosomes typically fuse with lysosomes to form phagolysosomes, which enable the degradation of the engulfed particles using specialized enzymes that work at low pH. In contrast, the primary function of basophils, a type of granulocyte, is to release chemical mediators such as histamine that enhance the immune response. Released histamine causes vasodilation and permeability of vessels, which stimulates an inflammatory response by increasing blood flow and the delivery of immune cells (eg, neutrophils and macrophages) at the site of infection. Therefore, during a parasitic infection, macrophages function to phagocytose organisms and basophils release histamine. (Choice A) The answer choices here are reversed. Although it has been noted that basophils can perform phagocytosis and macrophages can release histamine, these processes are uncommon. As a result, the reverse (macrophages, basophils) is the most likely answer choice. (Choices B and D) Natural killer cells are cellular components of the innate immune system. Natural killer cells release toxins to destroy body cells, such as neoplastic and virus-infected cells, that have reduced expression of major histocompatibility complex molecules. T-cells are cellular components of the adaptive immune system. T-cells are important in mediating a number of immune responses, including those against viruses. These types of cells are not known to directly phagocytose bacteria. Educational objective: Macrophages are one of the cells responsible for phagocytosis, the process of engulfing solid particles (eg, bacteria) designated for destruction into phagocytic vesicles called phagosomes. In contrast, basophils function to release chemical mediators such as histamine that stimulate an inflammatory response.

During a Parasitic Infection, Which of the Following Would Most