Complement C3 and C4

[MudPhud20XX]

---

Members don't see this ad.

So FC says in Rheumtoid Arthritis you get decreased C3 and FA says in SLE you get both decreased C3 and C4 due to the formation of immune complex. Can anyone just explain about this diff? When do you we get both decreased C3 and C4 and when do we get just decreased C3? Many thanks in advance.

 

[worldbeater]

I got a question recently wrong with SLE and it mentioned only C3 dropping, for what its worth.

 

[MudPhud20XX]

Interesting.... FA 15 on page 433 clearly says "decreased C3, C4, and CH50 due immune complex formation. Any thoughts??

 

[Jabbed]

Complement activation in autoimmune disease has two sides to it:

1. Self-antigen-antibody complexes form and complement system proteins are consumed in the clearance of the antibody-tagged antigens.
2. Isolated early complement deficiencies (C3 specifically) result in decreased clearance of self-antigens from circulation and thus increase the risk of an autoimmune reaction developing against these self-antigens.

Random thought: Decrease in several complement proteins (C3 and C4) probably result from situation 1. Isolated decreases in C3 can result from situations 1 or 2.

 

[Phloston]

So FC says in Rheumtoid Arthritis you get decreased C3 and FA says in SLE you get both decreased C3 and C4 due to the formation of immune complex. Can anyone just explain about this diff? When do you we get both decreased C3 and C4 and when do we get just decreased C3? Many thanks in advance.

I got a question recently wrong with SLE and it mentioned only C3 dropping, for what its worth.

Complement activation in autoimmune disease has two sides to it:

1. Self-antigen-antibody complexes form and complement system proteins are consumed in the clearance of the antibody-tagged antigens.
2. Isolated early complement deficiencies (C3 specifically) result in decreased clearance of self-antigens from circulation and thus increase the risk of an autoimmune reaction developing against these self-antigens.

Random thought: Decrease in several complement proteins (C3 and C4) probably result from situation 1. Isolated decreases in C3 can result from situations 1 or 2.

Another one of those things where the USMLE answer doesn't mean in real life it's the only answer. For some magical reason, test-writers became fixated on SLE = C3 = three letters; in cryoglobulinemia there can be decreased C4. Often times the clinical picture doesn't fit C3/C4, and a CH50 panel is ordered, which looks for heaps of different complements, since people's immune responses vary.