Antibodies are part of humoral immunity. The humoral pathway protects against extracellular pathogens. Antibodies are produced and secreted by B lymphocytes (B cells). They recognize free antigens, initiate activation of other immune cells, and coat the antigen for destruction (which may or may not be cellular). 

An AB positive patient is known as a universal recipient because they can receive blood from any blood type. The recipient's antibodies are what will attack foreign antigens. Type AB positive patients produce no antibodies, because any antibody produced would attack their own antigens, causing agglutination. Because type AB patients patients do not produce antibodies, they cannot attack any antigens and they can receive any blood type.

The two types of immune reactions found in the human body are the innate and adaptive immune systems. The innate immune system is the first defense for common antigens that enter the body, and will respond to any and all foreign antigens that it detects. The adaptive immune system utilizes antibodies to fight antigens that reappear in the body during subsequent exposures, and allows the system to more uniquely attack the specific antigen. Both systems can respond to a variety of different pathogens, including bacteria and viruses.

The heart is the only organ listed that is not involved in the immune response. The thymus is the site of T-cell maturation, while bone marrow is the site of B-cell maturation. The lymph nodes and spleen are sites of blood filtration to ensure that there are no pathogens in the system.

The innate immune system is the general, non-specific response to pathogens. It does not involve a memory component. The adaptive immune system is the more complex, specific response to pathogens. The adaptive immune system takes longer to develop, is able to discriminate between self cells and non self cells, and has a memory component so the second reaction is a quicker response to infection. 

The thymus is one of two primary lymphoid tissues and is the site of T cell processing, and maturation. These cells are sometimes referred to as thymocytes. The bone marrow is the other primary lymphoid tissue and is the site of B cell maturation. 

Tissues of the immune system are classified as central (primary) or peripheral (secondary). Peripheral tissues initiate adaptive immune responses. Peripheral lymphoid organs include: lymph nodes, spleen, and the mucosal and cutaneous immune systems (ex: peyers patches in the gastrointestinal tract).

Basophils are part of the innate immunity, and are a key player for stimulating inflammation. Basophils release histamine, which dilates blood vessels and increases the permeability of capillaries. This allows an infection to be walled off in the affected area and helps other white blood cells migrate to the area.

Eosinphils are involved in parasitic immunity and allergic reactions. Neutrophils, macrophages, and monocytes are responsible for phagocytosing foreign pathogens. B-lymphocytes release antibodies against a specific antigen.

White blood cells can be classified by whether or not they have granules in their cytoplasm (granulocytes and agranulocytes). There are three types of granulocytes, and all of them end in the suffix "-phil." Neutrophils, basophils, and eosinophils are considered granulocytes. Lymphocytes are agranulocytes, and do not have granules present in their cytoplasm.

The white blood cells are typically categorized into several major types. Each of these types have specific roles in the body, and their proportions will change during specific body conditions. Basophils are used to dilate blood vessels by releasing histamine and eosinophils become elevated during parasitic infections and allergy season. Neutrophils play an important role in recruiting other immune cells to damaged tissues. Lymphocytes include B-cells and T-cells and are involved in the adaptive immune response. Monocytes are the preliminary cells that differentiate into macrophages, which are involved in non-specific phagocytosis.