Immunohemolytic anemias part-2

Hello readers, here is the continuation of the previous topic, Immunohemolytic anemias. Today we will discuss the next two types, its more like winter special.

B) Cold agglutinin type-  Cold agglutinin derives their name from the fact that they show maximal activity at temperature lower than normal body temperature.
It is present in low titres in healthy individuals.
Physiological cold agglutinin develops naturally after birth as a result of change in expression of Red cell antigens and reacts maximally at 4°C.
While pathological cold agglutinin maximally reacts at around 28-31° C and tend to occur at very low titres.

Mnemonic is "Cold MILL"
C     -  Complement mediated hemolysis. 
         
M    -  IgM is the causative antibodies

  I     -  Cold agglutinin antibodies appear  
           transiently following Infections 
            [Mycoplasma pneumoniae, EBV,
            HIV, influenza virus, CMV]
          - I antigen is the most common
              target
           
L     - Chronic cold agglutinin AIHA is
          associated with Lymphoid 
           neoplasm
          (esp B cell neoplasm), leukemias     
           like CLL

Mechanism- IgM binds to red cell where the temperature may fall below 30°C. It agglutinates red cells, and fixes complement rapidly. As blood recirculates and warms, IgM is released,but sufficient deposition of complements leads to phagocytosis of affected red cells in spleen, liver, bone marrow.

Clinical presentation- Exerts their pathological effects either via hemolysis and red cell destruction in RE system predominantly liver or by vaso occlusion due to agglutination.
-Mild anemia, purplish discoloration of fingers, toes, earlobes [ Acrocyanosis],  mild hepatospleenomegaly,
Raynaud phenomenon in peripheral cold exposed parts.

C) Cold hemolysin type -
Also known as paroxysmal cold hemoglobinuria.
It's a rare fatal disorder causing intravascular hemolysis and hemoglobinuria when auto antibodies binds to P blood group antigens in cool, peripheral regions of body.

Paroxysmal Cold HemoGlobinuria:
P- P blood group antigens
C- Complement mediated lysis occurs.

    IgGs auto antibodies binds to red cell in  
    cool peripheral regions, Complement
    mediated lysis occurs when affected
    red cell recirculates to warm regions,
    because complement cascade 
    functions
    more efficiently at 37°C

H- Hemoglobinuria
G - Auto antibodies belong to class IgG

Symptoms of the patients aggravates on exposure to cold.

Winter is coming, we know what's coming with it.
Stay warm :)