Question

what does the immune system protect the body against?
changes of the internal body temperature
changes in the temperature of environment
changes caused by harmful pathogens
changes in the ph of the blood

Explanation:

The immune system's primary function is to defend the body against harmful microorganisms (pathogens) like bacteria, viruses, etc. Internal body temperature regulation is by thermoregulatory mechanisms, environmental temperature changes are not countered by the immune system, and blood pH regulation is via buffering systems. So the immune system protects against changes caused by harmful pathogens.

Answer:

changes caused by harmful pathogens