Eosinophils primarily mediate reactions to parasitic infections, including worms. Neutrophils respond to bacterial infections, and basophils to allergies (IgE). Megakaryocytes are responsible for making platelets.

Basophils and mast cells are responsible for secreting factors like histamine in response to allergens and drugs. Release of the histamine can cause throat constriction, hives, and inflammation. Eosinophils mediate reactions to parasitic infections and neutrophils to bacterial infections. Megakaryocytes produce platelets.

Neutrophils contain antimicrobial products in vesicles, which are secreted when they come into contact with foreign cells. Neutrophils primarily mediate reaction to bacterial infections and are the primary component of the white pus found in bacterial inflammation. Eosinophils respond to parasitic infections and basophils to allergies (IgE). Megakaryocytes produce platelets.

The granulocytes that participate in innate immunity have vesicles filled with chemicals and proteins, such as perforin and trypsin, that are released to kill foreign bacteria, fungi, and parasites. The granulocytes include neutrophils, eosinophils, basophils, and mast cells.

Neutrophils are involved in bacterial infections and eosinophils in parasitic infections. Basophils and mast cells are involved in allergic reactions and inflammation.

Macrophages are responsible for ingesting and degrading bacteria and viruses, and presenting their antigens on major histocompatibility complexes (MHCs) to B- and T-cells. Macrophages are thus responsible for mediating the initiation of an immune reaction.

Megakaryocytes produce platelets, and B- and T-cells are the lymphocytes to which macrophages present ingested antigens.

Megakaryocytes are responsible for producing platelets, the remnants of cells that help form clots.

B-cells and T-cells are responsible for humoral and cell-mediated immunity. Macrophages ingest bacteria and viruses and present them to B- and T-cells to initiate an immune reaction.

Plasma cells are differentiated B-cells that serve to secrete antibodies after being stimulated by a helper T-cell.

Natural killer cells are also stimulated by helper T-cells and secrete perforin to kill invading pathogens. Memory B-cells are differentiated B-cells that are specialized to detect a re-infection by the same pathogen, allowing for a quick immune response. Macrophages ingest infecting agents.

Endosomes function to shuttle phagocytosed material to the lysosome, where cellular digestion can take place. This means that professional phagocytes, such as macrophages, can be expected to have a larger number of endosomes than other cells that are less specialized for this process.

The role of a plasma cell in the immune system is to produce antibodies. These antibodies are effective in binding to extracellular pathogens. Antibodies produced by plasma cells would not be effective in binding to intracellular pathogens, such as M. tuberculosis and intracellular HIV. Only one answer choice specifies an extracellular pathogen.

Plasma cells are developed from B-lymphocyte precursors in response to the presence of a specific antigen, and are part of the adaptive immune response. As such, they would be relatively ineffective at fighting a newly-evolved microbe to which the body has never been exposed before.

Both B-lymphocytes and T-lymphocytes are derived from lymphoid progenitor cells, a division of hematopoietic stem cells. These progenitors are housed in red bone marrow. B-lymphocytes remain in the red bone marrow to mature, but T-lymphocytes transition to the thymus for positive selection.

The lymph nodes and spleen are secondary immune tissues, responsible for housing mature B- and T-lymphocytes in order to carry out the immune response. The lymph nodes and spleen are not responsible for immune cell development. Yellow bone marrow is primarily used for fat storage and is not involved in the lymphatic system or immune response.