Fig. 1. Proposed spectrum of antibody-derived immunity in oropharynx to explain the range of phenotypes observed in children¹⁷.

In humans resistant to Strep A pharyngeal acquisition (first column), antibodies may inhibit adhesion and encourage opsonophagocytosis of bacteria before colonisation is established. In this situation antibodies targeting bacterial virulence factors and toxins may or may not be present. Colonised humans likely do not block adhesion with antibodies but, at least for some time, can limit the proliferation of bacteria. Shedders often have heavy colonisation but may inhibit symptomatic infection by controlling bacterial virulence factors. In most cases, pharyngitis is superficial and self-limiting, but can also develop into systemic illness including Scarlet fever (final column), which has been linked to toxins including superantigens⁹⁴. The antibody symbols (blue) indicate where antibodies inhibit bacterial function, the crosses (red) where antibodies are lacking and no symbol where there is no requirement for antibodies. Created with Biorender.com.