The spleen is located in the upper left area of the abdomen, behind the stomach, and under the diaphragm. The main function of the spleen is to filter the blood. Healthy red blood cells easily pass through the spleen; however, damaged red blood cells are broken down by macrophages large white blood cells specialized in engulfing and digesting cellular debris, pathogens and other foreign substances in the body in the spleen.
The spleen serves as a storage unit for platelets and white blood cells. The spleen aids the immune system by identifying microorganisms that may cause infection. In addition to the lymph nodes and spleen, mucosal associated lymphoid tissues MALTs and gut associated lymphoid tissues GALTs play a vital role in the immune system, although they are considered to be part of the lymphatic system. MALTs are lymphoid tissues found in parts of the body where mucosa is present, such as the intestines, eyes, nose, skin and mouth.
They contain lymphocytes and macrophages that defend against pathogens attempting to enter from outside the body. Many cells work together as part of the innate non-specific and adaptive specific immune system. Immune cells are sometimes called white blood cells or leukocytes. Figure 2. Blood Cells. Granulocytes are a type of leukocyte that contain granules in their cytoplasm containing enzymes.
Neutrophils, basophils and eosinophils are types of granulocytes. Neutrophils are considered the first responders of the innate immune system. Neutrophils and macrophages circulate though the blood and reside in tissues watching for potential problems. Cells of the adaptive immune system also called immune effector cells carry out an immune function in response to a stimulus.
Natural killer T lymphocytes and B lymphocytes are examples of effector cells. For example, activated T lymphocytes destroy pathogens via cell-mediated response. Activated B cells secrete antibodies that aid in mounting an immune response. Effector cells are involved in the destruction of cancer. Figure 3.
Non-effector cells are antigen-presenting cells APCs , such as dendritic cells, regulatory T cells, tumor-associated macrophages and myeloid-derived suppressor cells. Non-effector cells cannot cause tumor death on their own. Non-effector cells prevent the immune action of the effector cells. In cancer, non-effector cells allow tumors to grow.
Tumor antigens can trigger adaptive immunity. Cells, such as macrophages, dendritic cells and B cells, that can process protein antigens into peptides. They are the major components of pus and are found around most common inflammations.
Their job is to eat and destroy foreign material. Basophils and eosinophils are white blood cells that contain large granules inside the cell. They interact with certain foreign materials. Their increased activity may lead to an allergic reaction.
The immune response is a coordinated effort. All of the immune cells work together, so they need to communicate with each other.
They do this by secreting increased levels of a special protein molecule called cytokines that act on other cells.
Eosinophils also play a role in fighting off bacteria. They are very important in responding to parasitic infections such as worms as well. They are perhaps best known for their role in triggering allergy symptoms. Eosinophils can go overboard in mounting an immune response against something harmless. For example, eosinophils mistake pollen for a foreign invader.
However, there are high concentrations of eosinophils in the digestive tract. These cells are perhaps best known for their role in asthma. However, they are important in mounting a non-specific immune response to pathogens, organisms that can cause disease.
When stimulated, these cells release histamine, among other chemicals. This can result in inflammation and narrowing of the airways. Lymphocytes are also essential in the immune system.
They come in two forms: B cells and T cells. Unlike other white blood cells that provide non-specific immunity, B and T cells have specific purposes.
B lymphocytes B cells are responsible for humoral immunity, which is the immune response that involves antibodies. B cells produce the antibodies that "remember" an infection. They stand ready in case your body is exposed to that pathogen again. T cells recognize specific foreign invaders and are responsible for directly killing them. B lymphocytes play a key role in the effectiveness of many current vaccines. In some cases, such as tuberculosis and pertussis vaccines, T lymphocytes are the main players.
Monocytes are the garbage trucks of the immune system. Their most important function is to clean up dead cells in the body. Leukocytes, better known as white blood cells, take on different forms that perform different roles in the immune system. These include:. White blood cells begin in the bone marrow in a process called hematopoiesis.
All blood cells descend from a common hematopoietic stem cell HSC. This is also called a "pluripotent" stem cell. These stem cells differentiate—or specialize—in different stages. The HSC cell first separates into either a lymphoid or myeloid stem cell. The lymphoid stem cell gives rise to the lymphoid cell line. This is the family of cells that produces B cells and T cells. The myeloid stem cells give rise to cells called myeloblasts. These further evolve into macrophages, monocytes, neutrophils, basophils, and eosinophils.
Myeloblasts can also turn into red blood cells and platelets. A normal white blood cell count is usually between 4, and 10, cells per microliter mcL. Infections usually cause an elevated white blood cell count, but there are also other possible causes.
The sections below discuss these in more detail. Granulocytes are white blood cells that have small granules containing proteins. There are three types of granulocyte cells:. These are present when the body fights off chronic infections. According to an article in American Family Physician , the normal range per cubic millimeter of white blood cells based on age are:. Doctors may continually monitor white blood cells to determine if the body is mounting an immune response to an infection.
During a physical examination, a doctor may perform a white blood cell count WBC using a blood test. They may order a WBC to test for, or rule out, other conditions that may affect white blood cells. Although a blood sample is the most common approach to testing for white blood cells, a doctor can also test other body fluids, such as cerebrospinal fluid, for the presence of white blood cells.
The following are conditions that may impact how many white blood cells a person has in their body. Leukemia is a type of cancer that affects the blood and bone marrow. Leukemia occurs when white blood cells rapidly produce and are not able to fight infections.
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