The symbol that represents the pathogen is the star.
Model 1 shows an immune response to pathogens circulating in the bloodstream (pictured as stars). Once these foreign particles or pathogens, in general, are detected, a chain of immune reactions is triggered to attack the invader and protect the organism. The first line of the image shows the process of phagocytosis, where a phagocyte (cell of the immune system) engulfs and absorbs the pathogen and breaks it apart.