The article deals with the relevant problem of how conceptual metaphors function within popular science medical discourse. According to the cognitive linguistics' postulate, human reasoning is based on a metaphorical conceptual system and to study how this mechanism functions is an important task for linguistics. The purpose of the paper is a complex study of the realisation of the conceptual metaphor Immunantwort ist Kampf (“Immune response is fight”) in German popular science medical discourse. The presumption is that this metaphor can be defined as a compound metaphor and unfolds into particular cases of verbal metaphors on different levels. The data for the analysis are the works of cognitivists who develop the theory of conceptual metaphor (Lakoff, Grady, Fauconnier etc.). The study is novel in that it employs the method of conceptual metaphor's contextual modelling by Kövecses within the framework of discourse analysis which impact the functioning of the metaphor within discourse through its priming. The analysis revealed that the discourse and conceptual-cognitive contexts are relevant factors for conceptual metaphors within popular science medical discourse. They define the specifics of the communication situation and include previous texts on this topic and its established conceptual-metaphorical system. The study's outcome justifies the validity of the contextual model's use and proves that all relevant context types must be activated to achieve the needed pragmatical effect. Further research can focus on the functioning of this metaphor in other European languages to elicit the regularities of its realisation in different cultures.