The history of the DL antibody goes back to the 1900’s. It was one of the first recognized forms of immune mediated hemolysis and responsible for inducing Paroxysmal Cold Hemoglobinuria (PCH). PCH is a transient condition, meaning that it comes on when immunoglobulins (Antibodies) are formed in response to a viral, bacterial, or spirochete infection. Its history will suggest that there is an association between PCH and syphilis. In over 90% of the cases of PCH in early history, the patient was co-diagnosed with syphilis. Throughout the 1900’s the condition began to evolve and is now seen most commonly in children following some sort of infection. Although it should be noted that PCH is not limited to those of adolescent age. So what really is the Donath-Landsteiner antibody and how does it contribute to PCH?
Paroxysmal Cold Hemoglobinuria (PCH) is an autoimmune hemolytic anemia (AIHA). Autoimmune meaning that they are antibodies that have cross-reacted to attack the individuals own cells. Hemoglobinuria means that there will be hemoglobin present in the blood, which suggests intravascular hemolysis. PCH is one of the more common intravascular hemolytic anemias. Typical patients present with fever, chills, abdominal and back pain, and pronounced hemoglobinuria. PCH typically presents in children following and upper respiratory infection or immunization. These patients often have a rapidly progressing anemia with hemoglobins that can fall as low as 2.5 g/dL. Peripheral blood smears show significant red blood cell agglutination and anisocytosis and poikilocytosis. Anisocytosis indicating variance in size of the red blood cells and poikilocytosis indicating variance in structure to the red blood cells. Schistocytes, spherocytes, and polychromasia are common findings. The spherocytes and polychromasia are indicative of the bone marrow trying to replenish the red cell population as best it can so it forces out immature erythrocytes into the peripheral blood. Its an effort to sustain the hemoglobin as best it can. One distinguishing peripheral blood smear finding in patients with PCH is erythrophagocytosis. Lets break this word down. Erythro- short for erythrocyte meaning red blood cells. Phagocytosis is mediated by neutrophils and monocytes as a way to kill foreign pathogens. In the case of erythrophagocytosis in PCH, neutrophils are characteristically seen engulfing red blood cells, which is diagnostic for AIHA.
The Donath-Landsteiner Antibody
The DL antibody, although being recognized as an cold autoantibody, is an IgG antibody that has developed P antigen specificity and it is a biphasic hemolysin. What that means is that when someone has the DL antibody and is exposed to cold temperatures, it will bind to the individuals red blood cells through the P antigen, but does not cause hemolysis until the coated red blood cells are heated to 37 degrees Celsius as they (RBC:antibody complex) travel from the peripheral fingertips and toes to the core of the human body. At cold temperatures, the IgG molecule is able to recruit complement (C3), and at the higher temperatures, activates the membrane attack complex (C5-C9) and lyses the red blood cells. One very interesting piece of information regarding the difference between Cold Agglutinin Syndrome (CAS), another autoimmune hemolytic anemia caused by Anti-I, is that the hemolysis from PCH is stronger and more severe because of the DL antibodies ability to detach from lysed red blood cells and reattaching to other cells.
There are a few different ways to pinpoint PCH in the blood bank. One is by use of a Direct Coombs test (DAT). This test provides information regarding the type of hemolysis, whether it be acquired or inherited. It also tests for antibodies that have are bound in vivo. The most common DAT result in PCH is red blood cells coated with C3d causing a positive reaction. This is sensitive in 94-99% of cases. The other way to diagnosis DLAIHA (Donath-Landsteiner Autoimmune Hemolytic Anemia) is by the indirect DL test. This process involves collection of a fresh serum specimen that is strictly maintained at 37 degrees Celsius from collection all the way through to testing. If the sample is allowed to cool or is refrigerated, there could potentially be autoadsorption of the DL anti-P antibodies onto the patients autologous red blood cells. This could cause a false negative result. Upon testing, the patients serum is mixed with P antigen positive, group O red blood cells, and fresh donor serum. The fresh donor serum is added because the complement level within the patients may be low due to consumption. The patient and donor serum mixture is incubated in a melting ice bath (O degrees Celsius) for 30 minutes, then warmed to 37 degrees Celsius for one hour. The specimen is then centrifuged and examined for hemolysis. If hemolysis is present then this constitutes a positive result for DL antibody.
Indirect DL test: As you can see in tubes 1 and 4, the presence of hemolysis indicates a positive test result for the DL antibody.
There is unfortunately no cure for PCH, and very little reliable treatment options for those with the DL antibody. It is recommended to avoid cold climates as much as possible and when inside to have the temperature at 30 degrees Celsius to keep the hemoglobinuria low. This doesn’t treat the PCH, but it will minimize the recurrence and induced anemia. Steroids have been through extensive trials for treatment of PCH and there are mixed results. Theory is that steroids are better at clearing red blood cells coated with IgG, and less effective at clearing red blood cells that are coated with complement. More aggressive treatment such as splenectomy and Rituximab, which is an monoclonal antibody that targets the transmembrane protein CD20 present on B cells has been found effective for those patients with refractory PCH.