Hematopoietic Stem Cell:
In spite of only a brief appearance (at the mess table in Episode 2) in our series, this character is the grand matriarch of all the cells of the immune system. She spends her entire life indoors (inside the bones), dedicating herself completely to generating an enormous number of descendents. Hematopoietic stem cells are undifferentiated, but when they divide can give rise to a large variety of cell types among which are other categories of more specific and fixed stem cells:
Erythroblasts — give rise to erythrocytes (red blood cells)
Granuloblasts — give rise to granulocytes
Lymphoblasts — give rise to lymphocytes
Monoblasts — give rise to monocytes, macrophages and dendritic cells
Megakaryoblasts and megakaryocytes — give rise to platelets
The above stem cell types produce all of the cells found in the blood (red blood cells, platelets and white blood cells), among which are the cells of the immune system. Hematopoietic stem cells are also known as colony forming units or hemocytoblasts
Lorris Temcell (lymphoid stem cell; lymphoblast):
This energetic cell is the mother of all the body’s lymphocytes, among which are some of our main protagonists, Johnny B. Goode and Julian Tivirus. Be careful not to confuse the terms lymphocyte and leukocyte: leukocyte refers to any of the cells of the immune system, while lymphocytes are a class of leukocyte. In contrast to hematopoietic stem cell, this type of stem cell is more specific and gives rise only to lymphocytes.
These cells are capable of multiplying time and time again, a process through which they manage to maintain a constant production line of lymphocytes over the course of their lives. At the same time they suffer the tragedy of witnessing the passing away of the great majority of their offspring at Bone Marrow High or Thymus Military Academy, where death awaits those who fail to make the grade . . . Just like their progenitors, hematopoietic stem cells, lymphoid stem cells are denizens of the bone marrow throughout their long lives.
Johnny B. Goode (future B-lymphocyte):
Johnny is a wet-behind-the-ears lymphoid precursor who attends Bone Marrow High where he is learning to be a B-lymphocyte. These cells, after being born in the bone marrow require a long period of schooling, and it is only after this that they are let loose into the bloodstream to defend the body. Like his classmates, Johnny B. Goode spends much of his time swatting up, but he also needs to see a bit of the world and meet other types of immune cells before he learns his trade. Therefore, his education requires him to travel outside the bone marrow, like a young Byron on his grand tour.
B-lymphocytes are the cells that produce antibodies, molecules whose role is both to detect (which they do with great accuracy) and eliminate threats. In this latter role they function much like guided missiles. Each B-lymphocyte is specialized in dealing with only one type of threat, to which it responds with great efficiency.
Tim Munity (T-Lymphocyte):
Tim is Johnny B. Goode’s grandfather. He left the bone marrow to enroll in the army and live a life of adventure. Little did he imagine that basic training at Thymus Military Academy would constitute a continuous threat to his very life. It’s been a hard-fought struggle but Tim has managed to best all that they’ve thrown at him at the Academy. His experiences there have been so traumatic, however, that he decides to record them for posterity in a diary, which, through pure coincidence, is found by his grandson.
Tim is a future T-lymphocyte — a type of lymphocyte who, despite being born in the bone marrow, is only able to fully develop in the thymus, following a long process of maturation. During this process, the majority of Tim’s comrades meet their end. In common with B-lymphocytes, but unlike other cells such as macrophages, NK cells and granulocytes, each T-cell recognizes only one threat, but to which it responds with deadly efficacy.
Alison Specific (Future Macrophage):
Alison is a monocyte who was born in the bone marrow and has left her home to work with great gusto as a circulating macrophage. Macrophages work in a non-specific manner (Alis-on Specific — geddit?!) against all types of foreign invaders, which they eliminate by gobbling them up — phagocytizing them. They also produce molecules called cytokines, which alert other cells to possible danger.
(Please note: Alison is a rare bird of the macrophage world, given that recent studies show that the majority of tissue macrophages do not derive from monocytes formed in the bone marrow, as was her case. There are macrophage precursor cells in every tissue and these give rise to macrophages in a bone marrow-independent manner. It is only when there is an attack that monocytes from the bone marrow are recruited to the site of the threat in order to beef up numbers.)
Julian Tivirus (natural killer [NK] cell):
Julian is a cell with an enormous desire to enter the bloodstream and begin his search and destroy mission for infected or cancerous cells. He is not yet quite fully trained up, though, to take the jump and leave his native bone marrow behind. You see, he has not yet had the chance to practice his “moves” — his innate abilities to destroy damaged cells — but this will come soon. Julian’s “ammunition” consists of molecules (granzyme, perforin) capable of generating pores in the membranes of target cells, which is lethal for them. Just like macrophages, NK cells release molecules that inform other immune cells of the presence of undesirable elements.
Francis Tamine (granulocyte):
Francis is a granulocyte who, together with Julian Tivirus and Alison Specific, leaves his birthplace in the bone marrow shortly after being born, forsaking comrades such as lymphocyte, Johnny B. Goode, who remain behind to complete their studies.
A granulocytes is a type of cell that defends us in a non-specific manner from whatever they perceive to be a threat. Its name comes from the quantity of granules it contains, and which are like bombs jam-packed with molecules, some of which are able to take out invading cells, and others which prepare the battle ground for the arrival of more specialized troops.
There a various types of granulocyte — neutrophils, eosinophils and basophils — whose names derive from the color they display after they are stained and observed under the microscope. We still don’t know what kind of granulocyte Francis will turn out to be . . .
Teachers Jules Troma, Fifi Broblast and Cosme Dullar:
Various teachers are responsible for the education of Johnny B. Goode and other B-lymphocytes in Bone Marrow High. This is the strictest bunch of teachers that ever darkened the door of a classroom. The tiniest mistake on behalf of a student is invariably met with apoptosis — in other words, death. Thanks to these teachers, though, Bone Marrow High has an enviable reputation for sending elite graduates out into the world — high caliber professionals who would never make the mistake of attacking the body’s own tissue.
These teachers, made of stern stuff, are all bone marrow stromal cells, and were born and raised in the bone marrow, where they now dedicate their lives to the noble cause of educating B-lymphocytes. (Stroma referrers to the cells and other components that make up the structure or scaffolding of any tissue. But, as you can see, stromal cells can have many more functions that the purely structural).
This inflexible instructor is the principal of Thymus Military Academy, from where only the cream of T-lymphocytes graduate. Olerance is a thymus stromal cell and ensures that lymphocytes properly develop the full range of their abilities and do not attack the body. Slow learners are dealt with ruthlessly — they are killed. That’s the law of the thymus.