Final answer:
Fimbriae and pili are bacterial structures that impact host immune system effectiveness by aiding in pathogenic bacteria adherence to host tissues.
Explanation:
Fimbriae and pili are thin, protein tubes that allow bacterial cells to attach to surfaces, including host cells. These structures directly impact the effectiveness of the host immune system by aiding in the adherence of pathogenic bacteria to host tissues, promoting colonization, infectivity, and virulence.
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