Reactivity of human antibodies with endogenous pgp3 in immunoprecipitation. Various amounts of the pooled positive human antiserum was used to precipitate chlamydial endogenous antigens from L2S100 with or without prior heat treatments either at 56°C for 30 min or boiling for 10 min. The human antibody precipitates were detected with either the anti-pgp3 polyclonal (pAb; panel a) or anti-CPAF monoclonal (clone 100a, panel b) antibodies as shown on the left of the figure. The corresponding protein bands were indicated on the right of the figure. Note that although the human antibodies precipitated both the endogenous pgp3 and CPAF from the native L2S100, these human antibodies no longer reacted with pgp3 in boiled L2S100 sample but maintaining the ability to pull down CPAF.