> See also: > - Reference # Blood Cells Blood cells and their developmental precursors are collectively called **hematopoietic cells**. - Leukocytes (White Blood Cells) - Erythrocytes (Red Blood Cells) - Megakaryocytes **Leukocytes**, commonly referred to as **white blood cells**, are the largest contributors to the human immune system. https://en.wikipedia.org/wiki/Stem_cell Reticulocytes are immature red blood cells ## Hematopoiesis > See also: > - [[Stem Cells]] All blood cells begin as [[Stem Cells|hematopoietic stem cells (HSCs)]], or cells that are capable of differentiating in many different ways depending on what the body needs. - Sometimes called *hematopoietic progenitor cells (HPCs)* The process of differentiating these cells during their development is known as **hematopoiesis** and allows the human immune system to have a [[Cells of the Immune System|wide array of cells]] with unique roles and functions. It is important for the **hematopoietic stem cells (HSCs)** to undergo self-renewal so that their populations can be *maintained* and enough daughter cells can be provided to mature and differentiate later on. - This ability is what drives [[Transplants & Transfusions|bone marrow transplants]] A cell in the immune system is **terminally differentiated** if it has *become the final form* that it can develop into. ## Red Blood Cells (Erythrocytes) ## White Blood Cells (Leukocytes) #### Leukocyte Adhesion Molecules 1. Selectins: carbohydrate-binding lectins 2. Vascular Addressins: contain carbohydrate groups to which selectins bind 3. Integrins 4. Proteins in the immunoglobulin superfamily