“…Over the past few years, several genes involved in the biosynthesis of Hib LOS have been characterized (6,13,16,26,28,30,32), and some of these have been shown to be involved in expression of surface-exposed LOS epitopes. Four of these surface-exposed epitopes, defined by their reactivity with monoclonal antibodies (MAbs) 12D9, 6A2, 4C4, and 5G8 (9, 20), were first noted because of the correlation between phase variation of their expression and changes in the virulence potential of Hib (11,12). The spontaneous phase variation of the epitopes reactive with MAbs 12D9, 4C4, and 6A2 has been attributed to the presence of a repetitive DNA motif (5'-CAAT-3') located in the 5' region of some of the relevant genes; variable expression of these genes was directly correlated with the number of CAAT repeats (28).…”