CASE HISTORY Bobby,an 11-Year-Old Boy from Nebraska,suffered His Entire Life from Recurring

CASE HISTORY
Bobby,an 11-year-old boy from Nebraska,suffered his entire life from recurring life-threatening infections caused mostly by the Gram-positive bacteria Staphylococcus aureus and Streptococcus pneumoniae.His infections included meningitis,osteomyelitis (bone infection) ,and arthritis caused by S.pneumoniae,as well as episodes of septicemia and osteomyelitis and recurrent boils caused by S.aureus.Tests to find a cause for these recurring infections were initially disappointing.The results of all standard immunological tests were normal,including T-cell lymphocyte responses,blood antibody levels,and antibody responses to injected proteins and polysaccharides.This means his adaptive immune system was functioning.The numbers of monocytes/macrophages in his blood were also normal.However,pro-inflammatory cytokine levels (indicators of innate immunity) measured during the latest infection were considerably lower than expected.Further tests proved that Bobby inherited an innate immune defect in Toll-like receptor signaling.Currently,there is no cure for this immunodeficiency.To stem the tide of infections,Bobby was placed on long-term,preventive antibiotic treatment.
Which of the following best describes the portion of a pathogen recognized by Toll-like receptors?

A) specific antigens, particularly those on the surface of Gram-positive pathogens such as Streptococci
B) repeating nonself motifs such as peptidoglycan from Gram-positive organisms
C) major histocompatibility complex molecules on the surface of pathogenic cells
D) Toll-like receptors on the surface of pathogens, recognized by MAMPs on our immune cells