Why is sheep erythrocyte lysis considered as classical complement activation pathway, and rabbit as alternative one?
The complement system is an innate immune response which has three pathways - as shown in the image below.
The breakdown of red blood cells assesses the functional capacity of the complement system. This experiment is titled: &quot;Total complement activity&quot;, &quot;CH50&quot; or &quot;CH100&quot;. Is this what you're referencing?
Hemolysis of sheep red blood cells occurs via the classical complement pathway.

More information: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4360204/