Transcription
It's a series in hematology, and today's topic is immune hemolytic anemia. Hemolysis is due to an immunological process, such as an antibody or a complement. So, here is the question: is immune hemolytic anemia an intrinsic defect or an extrinsic defect? The answer is extrinsic; it's something from outside of the red blood cell, also known as extracorpuscular. Fine. Is it an intravascular hemolysis or an extravascular hemolysis? It depends. Okay, so we classify immune hemolytic anemia into three different subtypes.
One: Autoimmune hemolytic anemia. This is by far the most common subtype, and it's a type 2 hypersensitivity reaction. It can be either due to an IgM or an IgG. We call IgG antibodies warm antibodies, why? Because they work in your body temperature, 37 degrees Celsius or 98 degrees Fahrenheit, which is warm. Contrast that with IgM, called cold antibodies; they work at 4 degrees Celsius all the way up to room temperature, which is 23 degrees Celsius or 73 degrees Fahrenheit. That's number one: autoimmune hemolytic anemia.
Two: Drug-induced hemolytic anemia. This is very high yield for the boards. Three: Alloimmune hemolytic anemia. Okay, so what does L-M-U and mean? Okay, question: what's the single word that's common across different languages and cultures? The answer is hello. When you answer the phone, you say hello or hello. Okay, and when you answer the phone, you are talking to non-self. Nobody talks to himself on the phone, unless maybe he's schizophrenic. Okay, so allo means non-self; you're reacting to non-self antigens, such as in transplant.
Warm versus cold autoantibodies. I did your IgM which is which. How to know if IgG is the warm and IgM is the cold one? Okay, so students came up with this idea, which is pretty dumb: warm weather is great, warm IgG, and cold ice cream is yummy, so IgM is the cold. This is so terrible. What are you people talking about? Cold ice cream can also be great. Okay, can you imagine that you will remember this during the exam? Of course not. Here's a more brilliant idea: you draw a sun, which is of course warm, and then you draw a nice G in it, which is pretty circular, so IgG's are warm. How about the IgM? Of course, you know that the IgM autoantibody is a pentamer; it has five pieces called monomers, and this looks like a snowflake, which is cold. So IgGs are warm; IgMs are cold. You will never forget it. Enough with the ice cream; I'm on a diet now.
Pathogenesis: three processes; either IgG mediated hemolysis, IgM mediated hemolysis, or complement mediated hemolysis. Okay, let's start with IgG. You have your nice red blood cell covered with an IgG, and now comes the splenic macrophage to consume this red blood cell, this nice biconcave cell. When the macrophage starts eating parts of these tiny corners and edges, it will convert to a circular cell called a sphere outside. So hemolytic anemias, especially the immune type, can have spherocytosis. That's true. Okay, and this is an extravascular hemolysis, since we are talking about splenic macrophages.
IgM mediated hemolysis: to understand them, let's go to the third type, which is complement mediated. It can be either extravascular or intravascular. Now we have three different stories. Number one: your red blood cell is covered with C3b, part of the complement; the splenic macrophage recognizes this as abnormal and consumes it. Since splenic, it's extravascular. Story number two: your red blood cell is coated with C3b as well as IgG antibody, so the spleen consumes the red blood cell. This is also extravascular. Third story, which is common: you have the red blood cell coated with a lot of complement, C5 through C9, which is called the MAC. This is not anti-Microsoft; this is the membrane attack complex. We have talked about the MAC briefly in our discussion in paroxysmal nocturnal hemoglobinuria. We have talked about the complement for a while. This will be intravascular, of course, why? Because the MAC will insert some pores into the red blood cell to disturb the osmotic environment of the cell, and the red blood cell will die there at its place, intravascularly; it will never reach the spleen.
IgM mediated hemolysis: it depends on the degree of complement activation. If you activate the complement avidly, which means C5 through C9, this is avid; this is like a lot of C5, 6, 7, 8, 9, avid activation. Okay, you have reached the final process, which is the MAC. When you fix the complement avidly, it's an intravascular hemolysis. Avidly has an I; intravascular has an I; and IgM mostly will fix the complement avidly, so you have intravascular hemolysis. Okay, these are the different pathogenesis; not mutually exclusive, why? Because IgM doesn't mean that the IgM itself will destroy the red blood cell; the IgM can activate the complement system. So being an autoantibody doesn't mean that I'm not going to activate the complement. Okay, I'll see you in the next video when we will discuss the first type of immune hemolytic anemia, called autoimmune hemolytic anemia, or AIHA. Don't say I huh. Okay, stupid. See you then.