Question

Which one of the following complement system pathways is most likely to be activated on biomaterials implanted in a healthy human?

• A. classical pathway
• B. lectin pathway
• C. alternative pathway
• D. extrinsic pathway

Hint:

Ask which pathway needs neither a pre-existing antibody nor a specific sugar tag to switch on, since a fresh synthetic implant has neither.

Answer 1

The Correct Option is C

Step 1: Recall the three complement activation pathways.
The complement system can be switched on by three routes: the classical pathway, the lectin pathway, and the alternative pathway.
The classical pathway needs an antibody (IgG or IgM) already bound to an antigen before it fires.
The lectin pathway needs mannose-binding lectin to recognize specific sugar patterns (mannose residues) on a microbial surface.

Step 2: Apply this to a biomaterial implant.
A synthetic biomaterial (a polymer, metal or ceramic implant) placed in a healthy person has no pre-existing antibody against it, since the immune system has never seen this synthetic surface before.
It also does not usually carry the specific mannose sugar patterns that the lectin pathway looks for.

Step 3: Identify what actually happens on the biomaterial surface.
As soon as blood touches the implant, plasma proteins adsorb onto it within seconds (the Vroman effect). This adsorbed protein layer and the foreign surface itself hydrolyze complement protein C3 directly, without needing antibody recognition.
This spontaneous, antibody-independent, surface-triggered activation of C3 is exactly how the alternative pathway starts, so it is the pathway that dominates on an implanted biomaterial.

Step 4: Eliminate the remaining option.
Option (D), the "extrinsic pathway", is not a complement pathway at all. It is one of the two pathways of the blood coagulation cascade, so it does not belong in this list conceptually and can be ruled out right away.

Final Answer:
The alternative pathway is triggered directly by the foreign surface, without needing a specific antibody or sugar-recognition step, so it is the pathway most likely activated on a biomaterial in a healthy person.
\[ \boxed{\text{Alternative pathway}} \]