Security coverage apply to certain. types of work. If you are self-employed, you earn. Social Security credits the same way. employees do (one credit for each $1,260. in net earnings, but no more than four. credits per year). Special rules apply if. you have net annual earnings of less. than $400.
White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders.All leukocytes are produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell.onocytes and neutrophils are phagocytic. The number of leukocytes in the blood is often an indicator of disease, and thus the WBC count is an important subset of the complete blood count. The normal white cell count is usually between 4 and 11 Ã 10 9 /L.
These three types of leukocytes are even further divided into more specialized cells, each with their own unique task in the immune system. To learn more details about the immune system, see Additional Resources. How does your immune system know which cells to attack and which cells are part of your own body? Your immune system can recognize cells based on the proteins present on the surface of cells. Viruses, bacteria, and other foreign cells are recognized as being different from your own cells and are attacked by your immune system. Sometimes, one of your own cells changes, or mutates, giving the cell the ability to multiply continuously. Such mutations often are the cause of cancer.