Luetic Reaction

LUETIC REACTION, the luetin test, a skin reaction proposed by Noguchi in 1911 for the diagnosis of congenital, hidden, and tertiary syphilis. The reagent is an emulsion of a killed culture of *Spirochaeta pallida* (the so-called luetin). A pure culture of spirochetes was grown by Noguchi (from 6 to 12, 24, and 50 days at 37°C) under strict anaerobiosis on a liquid medium [serum with the addition of sterile tissue (placenta)] and a solid medium (ascitic agar with the addition of a piece of placenta). Preparation of luetin according to Noguchi: to the culture (from 5–6 strains) of spirochetes from the lower part of the solid medium, triturated in a mortar for several hours to a paste-like consistency, the aforementioned liquid medium with abundant growth of spirochetes is added, and thoroughly mixed to obtain a liquid emulsion; the latter is heated at 60°C (½ hour), after which Tricresol is added (to ½%); storage in the cold. When using luetin, it is diluted with an equal volume of sterile physiological solution. Noguchi's first experiments with the L. r. were performed on rabbits infected with syphilis. Injections of luetin into humans are made into the epidermis of the skin of the arm (0.07 cm³ for an adult and 0.05 cm³ for children); a small pale swelling that forms in this case disappears after 10–15 minutes; the control is an emulsion from the medium on which the culture of spirochetes is grown, but without seeding the latter; it is injected into the other hand. The phenomena of the skin reaction are divided by Noguchi into three forms: papular, pustular, and torpid. In the papular form, a dense papule (7–10 mm in diameter) appears 24–48 hours after injection, surrounded by a zone of redness; the size of the infiltrate increases over 4–5 days, after which it begins to decrease; the color of the papule takes a bluish tint; hardening disappears within 2–3 weeks. Pustular form: the beginning of the reaction resembles the previous form up to the 4th–5th day, after which the papule becomes edematous and is covered with pustules of various forms containing pus; after the pus is evacuated, a crust forms. Inflammatory phenomena gradually subside, and a slight scarred induration remains at the former site of the papule. Torpid form. In rare cases, a late reaction is observed (after 10–14 days). General phenomena in the L. r., with rare exceptions, do not occur. With a negative reaction, a slight erythema is observed at the site of the puncture after 24 hours, disappearing after 48 hours; sometimes, however, a negative reaction may give a small papule, which resolves on the 3rd day without a trace. The histological picture of sections from large papulo-pustules (in a positive L. r.) resembling softened gumma is as follows (Aristova): edema of the papillae is observed in places; the cells of the infiltrate are arranged along the course of vessels (superficial and deeper) and connective tissue sheaths of sweat, sebaceous glands, and hair follicles and form a polymorphous granuloma; the latter contains plasma cells, many mast cells, plasmoblasts, lymphocytes, and often giant cells; in small vessels, loosening of the walls, swelling of the endothelium, and the exit of lymphocytes and plasmoblasts are observed. In sections from cases with regression, proliferation of connective tissue is observed, often with abundant content of phagocytes. Based on histological data, it is justified to assume that luetin causes the formation of an unstable granuloma, analogous to the formation of a tubercle under the influence of spirochetes; the difference in stability and course depends on the fact that the L. r. is caused by a killed culture of spirochetes, while the infectious granuloma is caused by a live virus. Increased tissue sensitivity (sensitization), thanks to which an unusual reaction of the skin occurs upon the introduction of an antigen, in other words, the action of the antigen—luetin—on the antibodies formed in the body of the patient, causes anaphylaxis or skin allergy, which represents the luetin reaction (Noguchi). The L. r. has diagnostic significance mainly in tertiary, congenital, and hidden syphilis; in these stages it gives a high percentage of positive results: 95–100% (according to various authors); in syphilis I and II, most authors obtained a negative L. r., and only in isolated cases did the percentage of positivity reach 15–40 (mainly treated cases); in syphilis of the brain and nervous system, a positive L. r. is obtained in 60–80%. According to Noguchi, the L. r. is also a valuable method for prognosis: with a negative RW in a latent syphilitic, a negative skin reaction indicates recovery; in cases of long-standing syphilis with severe general symptoms and a positive RW, a negative L. r. gives a grave prognosis; this is especially observed in progressive paralysis. From what has been said, the absence of parallelism between seroreactions—RW and L. r.—becomes clear. Regarding the specificity of the reaction, the conclusions of authors who tested it diverge sharply: a few (Kafka) attach almost absolute value to it both for diagnosis, therapy, and prognosis in syphilis, considering its application indicated along with serum and liquor seroreactions; others consider it relatively specific. A few authors express themselves in favor of the absolute nonspecificity of the L. r. In view of the aforementioned disagreements, caused by the heterogeneity of the proposed luetin preparations, as well as the difficulty of obtaining a pure culture of spirochetes, the skin L. r. is rarely applied in practice (even in America).

LUIE