The antibody response against a spirochetal strain isolated from Swedish Ixodes ricinus ticks was determined by enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay of cerebrospinal fluid (CSF) and serum specimens from 45 patients with chronic meningitis. Samples of CSF, serum, or both from patients with various infections of the central nervous system, multiple sclerosis, syphilis, or infectious mononucleosis and from healthy individuals served as control samples. Probable spirochetal etiology could be demonstrated for 41 of 45 (91%) patients with clinical symptoms of chronic meningitis. Approximately 25% of the patients had significantly elevated titers of antibody to the spirochete in CSF but not in serum. The highest diagnostic sensitivity, 91 %, was demonstrated by measurement of CSF antibodies and calculation of a spirochetal CSF titer index, which is the ratio of (ELISA titer in CSF/ELISA titer in serum) to (albumin in CSF/albumin in serum) and which also considers the degree of blood-CSF barrier damage. The highest specificity, 98%, was obtained by calculation of a CSF titer index. Patients with short duration of disease were especially prone to be antibody negative in serum but positive in CSF. Significant rise in serum antibody titers was seldom demonstrated in patients treated with antibiotics. It is concluded that measurement of CSF antibodies, especially by ELISA, is a highly sensitive and specific method for the immunological diagnosis of spirochetal meningitis.

The enzyme-linked immunosorbent assay (ELISA) was applied for immunological diagnosis of human tularemia, using lipopolysaccharide from Francisella tularensis as antigen. Sera collected from patients, healthy individuals, and vaccinated volunteers were investigated for antibodies against F. tularensis by ELISA and tube agglutination. In ELISA all sera were titrated with a polyspecific anti-immunoglobulin enzyme conjugate. A limited number of consecutive sera from individual patients were also investigated for immunoglobulin G (IgG) and IgM antibodies by means of immunoglobulin class-specific conjugates. On an average ELISA was more than 10-fold as sensitive as tube agglutination. Two weeks after onset of disease, sera from patients had significantly higher titers in ELISA than sera from healthy controls. High titers persisted after more than 2 years. Significant amounts of both IgG and IgM antibodies were present within 1 to 2 weeks after infection. The antibody activity increased during the first month, without any significant change of the relation between IgG and IgM titers. After 2.5 years the IgG/IgM titer ratio of sera from patients was significantly increased. Within 6 weeks after vaccination sera from about half of the vaccinees had significantly elevated titers in ELISA. Titers observed after vaccination were generally lower than those found after infection. An elevated ELISA titer can be of diagnostic importance by the end of the first week of illness. A significant increase of titer in consecutive serum samples indicates a diagnosis of tularemia. Determination of IgG and IgM antibodies may be of value in determing whether a positive titer of a single serum sample is of longstanding or recent origin.

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SUMMARY. Antibody responses in human sera against Bordetella pertussis during natural infection were investigated by a microplate enzyme-linked immunosorbent assay (ELISA) with a purified fimbrial haemagglutinin preparation as antigen. Significant rises of specific IgG, IgM and IgA were demonstrated in paired sera. A secondary type of antibody response was found in most children and adults. In children, the type of response correlated with previous vaccination status; there was a primary response in unvaccinated children. A survey of antibodies in the general population showed low IgG titres in a small proportion of sera from the youngest healthy children. The titres and the number of individuals with measurable antibodies increased with age. In a limited study of the effect of vaccination, significant rises of titres were demonstrated after vaccination. The ELISA test was specific for antibodies against B. pertussis except that the test also seemed to measure antibody to B. parapertussis. A comparison between ELISA and the complement-fixation test showed a good correlation between the tests only in sera from children 1-12 years old.

1. A glycol‐chitin‐splitting enzyme without lysozyme (muramidase) activity was found in serum from various animals. Goat, cow, hen, sheep and pig possessed high activity. No activity was found in serum from man, monkey, horse, dog, cat, rabbit, guinea‐pig or hamster. 2. Glycol chitin has been used as a substrate in purification and characterization. A viscosimetric assay with the use of this substrate was found to be a convenient method. 3. By means of ammonium sulphate fractionation of goat serum and subsequent gel chromatography a 100‐fold purification of the enzyme was obtained. 4. The purified enzyme has its optimal activity around pH 1.65 with glycol chitin as a substrate and, when incubated at 50 °C for 60 min, the optimal stability is in the pH interval 3.5–6.5. The pI determined by isoelectric focusing is 4.85 and the molecular weight assessed by gel chromatography is around 60000. 5. The purified goat serum enzyme degrades colloidal chitin with an optimum at pH 5.5 and is thus defined as a chitinase. Goat anti‐human lysozyme serum does not inhibit the purified chitinase. 6. To elucidate the origin of the serum chitinase, the concentration of the enzyme was determined in various organ tissues and body fluids. The highest activity with the exception of serum was found in the wall of the fourth stomach of goat and cow.