PMN/Lymphocyte and Candida

[acciddropping]

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Can you explain why Neutropenia is associated with Candida and Aspergilosis but with fungal infection as in meningitis, lymphocytes are increased?

I am so weak on Immuno...
txks

 

[thehundredthone]

Neutrophils mediate immunity against both invasive Aspergillus and Candida. (Remember how NADPH oxidase deficiency can cause Aspergillosis? NADPH oxidase pathways exist within neutrophils) A key point to remember is that immunity against mucocutaneous candidiasis is T cell mediated, whereas that against systemic candidiasis is neutrophil mediated. Hence, Chronic Mucocutaneous Candidiasis is a T cell disorder and you do not have fungemia. This explains why there can be systemic Candidiasis or Aspergillosis in neutropenic states.

In most other sites and most other fungal infections, immunity is T cell mediated, hence the increase in lymphocytes.

 

[thehundredthone]

EDIT: Double post.

 

[acciddropping]

Neutrophils mediate immunity against both invasive Aspergillus and Candida. (Remember how NADPH oxidase deficiency can cause Aspergillosis? NADPH oxidase pathways exist within neutrophils) A key point to remember is that immunity against mucocutaneous candidiasis is T cell mediated, whereas that against systemic candidiasis is neutrophil mediated. Hence, Chronic Mucocutaneous Candidiasis is a T cell disorder and you do not have fungemia. This explains why there can be systemic Candidiasis or Aspergillosis in neutropenic states.

In most other sites and most other fungal infections, immunity is T cell mediated, hence the increase in lymphocytes.

I am going to repeat what you said and see if I get it right...... Asp and Candida are both Catalase positive and therefore, CGD patients get infection with those - NADPH oxidase is part of both Neutrophil and Macrophage killing mechanism ( therefore, Neutropenia state will result in infection with Asp and Candida where Candida is a systemic cause and not cutaneous cause). I think Macrophage has myeloperoxidase and macrophage does not...

Now, cutaneous Candida is eliminated by T - cells - why??! Does it have anything to do with Macrophage or type 4 Hypersen?!

Thanks!!

 

[thehundredthone]

You've approached it conversely to link up with that explanation, but more or less, yes. Immunity against most fungal infections including cutaneous candidial infections is T cell regulated. Immunity against systemic candidiasis is neutrophil regulated. Note that this is a simplified model specifically for the USMLE, and the real immune regulation against fungal infections is still being studied and includes both innate and adaptive immune responses.