Mast cells contains secretory granules, rich in histamine and other hormonal mediators, that promote inflammation and other allergy symptoms in response to antigen exposure.

The humoral response refers to the antiquated term "humors", meaning body fluids, as used in ancient and medieval medicine. In response to antigen exposure, B-cells release antibodies into the extracellular fluid and throughout the body, thus eliciting a "humoral response."

Although helper T-cells are responsible for activating B-cells, the humoral response is limited to B-cells because they are the ones releasing products into the body fluids.

Metastasis is the proliferation of cancer cells into new tissues. Cancer usually metastasizes through the circulatory or lymphatic systems, and the cancerous cells take residence in other, seemingly unrelated parts of the body.

Memory B cells circulate the body and are ready to respond to subsequent infections while plasma cells generate many antibodies to a current infect. "Immunoglobulins" refers to both the B cell receptor and to the excreted form of these proteins (known as antibodies). IgG is a class of immunoglobulins (along with IgA, IgE, IgD, and IgM). Finally, macrophages are cells that engulf non-self (and often antibody-bound) cells and communicate with T cells to promote B cell proliferation.

Red blood cells are made in the bone marrow, and live for about 3-4 months. They are enucleated (lacking a nucleus), which makes more space available for hemoglobin molecules, which function to carry oxygen to the tissues. HIV infects T-helper cells, which are white blood cells, not red blood cells. Thus, the name makes sense since the virus infects cells of the immune system (white blood cells) and causes immunodeficiency. The liver and spleen play roles in recycling the red blood cells once they have carried out their function for about 120 days.

Keratinocytes are not immune cells. Rather, they secrete a protein called keratin which is a large proportion of the extracellular matrix and makes up hair, nails, skin, and other parts of the body. All other cells are immune cells. 

B-cells produce antibodies (a subset of adaptive immunity called humoral immunity). The usual sequence involves B-cell activation via interleukins from helper T-lymphocytes, which cause the B-cell to undergo mitosis, creating numerous clones that will differentiate into plasma cells (rapid antibody producers) or memory B-cells. 

Antibodies (or immunoglobulins) are produced by B-leukocytes and plasma cells, and are a key part of humoral (having to do with bodily fluids) immunity. As such, they can be found in several of the fluids circulating or exiting the body. Some types of immunoglobulins can even cross the placenta or be secreted in breast milk to pass immunity from a mother to her child.

All of the given answer options describe mechanisms for immunoglobulin function.

Neutralization occurs when the antibodies simply cover the biologically active portion of the pathogen, rendering it harmless. Complement fixation refers to the antibodies binding to the pathogen and facilitating the activation of the complement system (a series of plasma proteins that activate other immune processes). Precipitation is when antibodies link the antigens on many pathogens together, creating an insoluble clump ready for removal.

The immune system is very adaptive. The body has many antibodies that will each recognize different antigens. If an antibody binds to an antigen, the antibody will be copied so that the body can quickly recognize the threat if it is exposed to the antigen a second time. This process is known as the adaptive immune response.

When an antigen is presented for a second time, antibodies to the antigen are released. These antibodies bind to the antigen, labelling it for attack by immune cells and preventing it from interacting the membrane proteins on the host cells.