Immunofluorescent staining for tyrosine phosphorylation in association with C. trachomatis L2 and D, C. muridarum (MoPn), C. caviae (GPIC), and C. pneumoniae (Cpn) EBs during internalization by HeLa 229 cells. Cultures at 1 h postinfection were costained by indirect immunofluorescence for EBs using a rabbit polyclonal antiserum and tyrosine phosphorylation with MAb 4G10. Tyrosine phosphorylation is not seen in association with C. muridarum, C. caviae, and C. pneumoniae EBs but is readily observed with C. trachomatis serovars L2 and D. Bar, 5 μm.