Growth and neutralization of the trachoma agent in mouse lungs

Reactivation of Chlamydia trachomatis lung infection in mice by cortisone

To study the latency, chronicity, and recurrent nature of chlamydial infection, we attempted to reactivate Chlamydia trachomatis lung infection in mice by immunosuppressive therapy with cortisone. Mice were treated with subcutaneous injections of cortisone acetate (125 mg/kg) every other day, starting on day 14 after intranasal inoculation of C. trachomatis serotype B (TW-5). C. trachomatis was recovered from the lungs beginning day 6 after the start of cortisone treatment until the end of the observation period on day 12 of treatment. Overall, the reactivation was successful in 8 of 55 mice treated with cortisone, in contrast to 0 of 41 inoculated, untreated mice (P = 0.009) and 0 of 35 uninoculated, treated mice. Cortisone treatment affected the ability of peritoneal exudate cells to respond to migratory inhibition after exposure to purified whole organisms of C. trachomatis serotype B (TW-5) but had little effect on serum antibody titers, indicating a possible role for cellular immunity in resistance against C. trachomatis infection in the lung.

Neutralization of Chlamydia trachomatis infectivity with antibodies to the major outer membrane protein

Rabbit immunoglobulin G (IgG) antibodies raised against the major outer membrane protein of the Chlamydia trachomatis lymphogranuloma venereum strain 434 neutralized the infectivity of the parasite for HeLa 229 cells. The mechanism by which anti-major outer membrane protein IgG prevented C. trachomatis from establishing infection was studied by using intrinsically 14C-radiolabeled elementary bodies. Neutralized elementary bodies were filterable through a polycarbonate filter (pore diameter, 600 nm), demonstrating that reduction in infectivity was not due to the aggregation of elementary bodies by cross-linking IgG. Antibody-neutralized elementary bodies attached to and penetrated HeLa cells at rats nearly identical to those for infectious organisms exposed to nonneutralizing control IgG. These results suggest that antibody interferes with the infectious process of the parasite after its internalization. Anti-major outer membrane protein Fab fragments could not be substituted for neutralizing IgG antibodies. The requirement for intact IgG implies that cross-linking of antibodies to the major outer membrane protein on the surfaces of the organisms may be instrumental in neutralization.

Inapparent respiratory infection of inbred Swiss mice with sulfadiazine-resistant, iodine-negative Chlamydiae

Three chlamydial strains were isolated from the lungs of three different strains of mice that were inbred for over 30 years. These chlamydial strains were resistant to sulfadiazine and did not induce iodine-positive, glycogen-like material in the inclusions of infected L cells which characterizes them as Chlamydia psittaci.

Inhibition by pyrimidine analogues of the synthesis of folic acid by trachoma agents

Trimethoprim, a 2,4-diaminopyrimidine derivative which inhibits the growth of some bacteria by interfering with folic acid synthesis, inhibited the growth of several strains of the trachoma agent. Inhibition was most clearly demonstrated by measuring prolongation of mean death time of groups of chick embryos inoculated with a single lethal dose of agent. Over a certain range, prolongation was proportional to the logarithm of concentration of inhibitor; higher concentrations were toxic for the embryo. On a weight basis, trimethoprim was not as active as sulphafurazole. Inoculation in conjunction with sulphafurazole resulted in slight potentiation of activity. A related pyrimidine derivative, the antimalarial drug pyrimethamine, also significantly inhibited the growth of one strain of trachoma.

In cell culture, trimethoprim decreased the number of inclusions formed by a suspension of the trachoma agent and induced morphological changes in the inclusions similar to those caused by sulphafurazole.

Inhibition of the growth of the trachoma agent in the chick embryo was reversed by leucovorin calcium. It is concluded that, as with bacteria, the drug acts by blocking the folio acid cycle and that the trachoma agent most probably contains a dihydrofolate reductase.

Immunogenicity of experimental trachoma vaccines in baboons. I. Experimental methods, and preliminary tests with vaccines prepared in chick embryos and in HeLa cells

Parallel titrations of a strain of trachoma (MRC–221) and one of inclusion conjunctivitis (MRC–4) in the baboon conjunctiva and in chick embryos suggest that ten to twenty 50% egg infective doses are equivalent to one 50% baboon infective dose; but that at least 1000 egg infective doses are needed to induce moderate or severe infections in all of a given number of baboons.

For vaccine experiments in baboons, a system of scoring physical signs and presence of inclusion bodies was devised; the significance of differences in vaccinated and control animals in their response to conjunctival challenge was determined by analysis of variance. An aqueous suspension of live MRC–4 grown in the yolk sac was given as two subcutaneous doses and one intravenous dose at weekly intervals, and protected all of six baboons challenged with the homologous strain; three similarly spaced subcutaneous doses were less effective. The immunity induced by this vaccine waned considerably during the ensuing 15 months. Vaccine prepared from a live ‘fast-killing’ variant of MRC–4 grown in HeLa cells was less effective than MRC–4 itself in protecting baboons against infection with the parent strain.

Although both yolk sac and HeLa cell vaccines induced the formation of antibody fixing complement with trachoma group antigen, the serum titres in individual animals at the time of challenge were unrelated to the degree of protection; during a 15 month observation period there were pronounced falls in the titres of antibody induced either by vaccination or by challenge with egg-grown TRIC agent.

We wish to thank Dr I. Sutherland (M.R.C. Statistical Research Unit) for his helpful advice during the early stages of this work. We are also greatly indebted to Mr P. Avis (Pfizer Ltd.) for his advice and for undertaking the statistical computations; and to Miss Anne Smith and Miss Pay Storey (M.R.C. Trachoma Research Unit) for doing the complement fixation tests.