Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Q: Abstract: Human IgG4 antibodies directed against phospholipase A, the P1 antigen from Dermatophagoides pteronyssinus extracts, and cat albumin were found unable to cross-link antigen. Previously, it was demonstrated that IgG4 antibodies, in contrast to IgG1 antibodies, did not cross-link Sepharose-bound antigen and antigen added in solution. To eliminate the possibility that this phenomenon was caused by preferential binding of both IgG4 Fab fragments to the solid-phase-bound antigen, cross-linking of antigen was studied in a fluid-phase system. In this test, incapability of IgG4 antibodies to bridge two antigens was also found. As a result of such a phenomenon, it is expected that immune complexes formed by IgG4 antibodies will be considerably smaller than complexes formed by IgG1. This was confirmed by analysis of the molecular size profiles of IgG1- and IgG4-containing immune complexes in sucrose-density gradients. Moreover, IgG1 was able to precipitate antigen in a radioimmunoprecipitation test, whereas precipitation was not demonstrable by the same amount of IgG4 antibodies. Even 3% polyethylene glycol 8,000 did not precipitate the small IgG4-containing immune complexes efficiently. The antibodies studied were of a high-affinity type, and there was no significant difference in association constants between IgG1 and IgG4 antibodies. Therefore, we were not able to confirm observations reported in the literature that the IgG4 subclass is associated with a low-affinity antibody response; probably, the affinity of the IgG4 antibodies was underestimated by other investigators because of the polyethylene glycol precipitation technique used to separate antibody-bound and free antigen. Our findings stress the point that IgG4 antibodies take a special place in the immune response upon chronic exposure to antigen.

A: Albumins
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Q: Abstract: The clinical, therapeutic, and histological features of 54 patients with medulloblastoma were analyzed retrospectively by a multivariate approach with regard to prognosis. The overall 5-year survival rate was 60%, with 48% of patients free of recurrence at 5 years. Cell differentiation, when present, was associated with a significantly longer recurrence-free period. Seventy-two percent of patients with the histological finding of cell differentiation were recurrence-free at 5 years. A marginally significant increase in the 5-year survival rate was also seen in association with differentiation. Only 34% of the patients whose tumor exhibited necrosis were alive at 5 years. There was no statistically significant difference in 5-year survival for children under 3 years of age or for the group of children aged 5 years or under. However, a significantly larger fraction (72%) of the group aged 5 years or under had a recurrence-free period of 5 years or more. Other factors including sex, extent of surgical resection. Chang tumor stage, posterior fossa radiation dose, and adjuvant chemotherapy did not influence prognosis.

A: Adolescence
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Q: Abstract: Thirty patients suffering from minor head injury were examined with auditory brain stem responses (ABR), neuropsychological tests for assessment of higher nervous functions, and a questionnaire on postconcussional symptoms. Comparison of the 6 patients with altered ABR with the other 24 showed no statistical difference in either the number of long-lasting postconcussional symptoms or the scores on neuropsychological tests. Subclinical brain stem involvement as shown by ABR does not seem to correlated with impaired mental function or symptoms of the postconcussion syndrome. This greatly limits the use of ABR in forensic medicine.

A:
Adolescence
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