Gender segregation in childhood: a test of the interaction style theory.

The authors investigated the play/interaction-style theory of gender segregation with a sample of 39 children aged 2 to 5 years (primarily Caucasian). According to this theory, children prefer playmates with styles of play or interaction that are similar to their own. Because such styles are sex differentiated, same-sex playmate preference (i.e., gender segregation) results. The authors observed children during free play to determine preferred playmates and gender segregation level, and they used teacher ratings to derive play/interaction-style scores. The authors used a multiple regression approach to path analysis to analyze effects of sex of participant, participants' play/interaction-style scores, playmates' play/interaction-style scores, and degree of gender segregation to determine their effects on one another. The authors observed significant levels of gender segregation, with highly aggressive or active children displaying less segregation than their peers did. However, gender segregation was not associated with a preference for playmates with similar play or interaction styles.

Molecular structure of staphylococcus and streptococcus superantigens.

Staphylococcus aureus and streptococci, notably those belonging to group A, make up a large family of true exotoxins referred to as pyrogenic toxin superantigens. These toxins cause toxic shock-like syndromes and have been implicated in several allergic and autoimmune diseases. Included within this group of proteins are the staphylococcal enterotoxins, designated serotypes A, B, Cn, D, E, and G; two forms of toxic shock syndrome toxin-1 also made by Staphylococcus aureus; the group A streptococcal pyrogenic exotoxins, serotypes A, B, and C; and recently described toxins associated with groups B, C, F, and G streptococci. The nucleotide sequences of the genes for all of the toxins except those from the groups B, C, F, and G streptococcal strains have been sequenced. The sequencing studies indicate that staphylococcal enterotoxins B and C and streptococcal pyrogenic exotoxin A share highly significant sequence similarity; staphylococcal enterotoxins A, D, and E share highly significant sequence similarity; and toxic shock syndrome toxin-1 and streptococcal pyrogenic exotoxin B and C share little, if any, sequence similarity with any of the toxins. Despite the dissimilarities seen in primary amino acid sequence among some members of the toxin family, it was hypothesized that there was likely to be significant three-dimensional structure similarity among all the toxins. The three-dimensional structures of three of the pyrogenic toxin superantigens have been determined recently. The structural features of two of these, toxic shock syndrome toxin-1 and enterotoxin C3, are presented. Toxic shock syndrome-1 exists as a protein with two major domains, referred to as A and B. The molecule begins with a short N-terminal alpha-helix that then leads into a clawshaped structure in domain B that is made up of beta strands.

Investigation of the role of the disulphide bond in the activity and structure of staphylococcal enterotoxin C1.

The goal of this study was to investigate the role of the disulphide bond of staphylococcal enterotoxin C1 (SEC1) in the structure and activity of the toxin. Mutants unable to form a disulphide bond were generated by substituting alanine or serine for cysteine at positions 93 and/or 110. Although we did not directly investigate the residues between the disulphide linkage, tryptic lability showed that significant native structure in the cystine loop is preserved in the absence of covalent bonding between residues 93 and 110. Since no correlation was observed between the behaviour of these mutants with regard to toxin stability, emesis and T cell proliferation we conclude that SEC1-induced emesis and T cell proliferation are dependent on separate regions of the molecule. The disulphide bond itself is not an absolute requirement for either activity. However, conformation within or adjacent to the loop is important for emesis. Although mutants with alanine substitutions were not emetic, those with serine substitutions retained this activity, suggesting that the disulphide linkage stabilizes a crucial conformation but can be replaced by residues which hydrogen bond.

Predictions of T-cell receptor- and major histocompatibility complex-binding sites on staphylococcal enterotoxin C1.

We have focused on regions of staphylococcal enterotoxin C1 (SEC1) causing immunomodulation. N-terminal deletion mutants lacking residues 6 through 13 induced T-cell proliferation similar to that induced by native toxin. However, mutants with residues deleted between positions 19 and 33, although nonmitogenic themselves, were able to inhibit both SEC1-induced T-cell proliferation and binding of the native toxin to major histocompatibility complex (MHC) class II. Presumably, these deletions define a part of SEC1 that interacts with the T-cell receptor. Three synthetic peptides containing residues located in a region analogous to the alpha 5 groove of SEC3 had residual mitogenic activity or blocked T-cell proliferation induced by SEC1 and appear to recognize the same site as SEC1 on a receptor for the toxin, presumably MHC class II. We conclude that isolated portions of the SEC1 molecule can retain residual mitogenic activity but that the entire protein is needed to achieve maximal superantigenic stimulation. Our results, together with the results of other investigators, support a model in which SEC1 binds to an alpha helix of MHC class II through a central groove in the toxin and thereby promotes or stabilizes the interaction between antigen-presenting cells and T cells.

Fracture of a fenestrated metal backing of a tibial knee component. A case report.

The case of a metal-backed tibial component that failed by metal fracture is reported. Fracture occurred through fenestrations in the metal plate surrounding the central metal stem. The fracture followed loss of bony support beneath the medial tibial plateau, which had allowed varus deformity of the replaced joint. A high tibial osteotomy procedure had preceded replacement of the joint.

[The effect of the pupil as aperture and field stop on the various components of the human electroretinogram (author's transl)]. / Die Wirkung der Pupille als Apertur- und Bildfeldblende auf die verschiedenen Komponenten des menschlichen Elektroretinogramms.

The electroretinogram (ERG) was recorded in 10 normal subjects under scotopic and photopic conditions with the pupil of one eye constricted and that of the other eye dilated. The human iris, being displaced from the nodal point of the eye, acts not only as an aperture, regulating the retinal illumination, but also as a field stop, limiting the visual angle, especially for large object fields, as in Ganzfeld illumination. This double effect of a constricted pupil clearly influences the Ganzfeld ERG, not only shifting the intensity response functions to higher luminances but also diminishing the maximal responses. Control experiments with smaller test fields, which are less affected by the pupillary field-stop properties, reveal no diminution of the scotopic b-wave amplitudes. Implicit time functions, being nearly independent of the number of receptors stimulated, can be matched by taking into account the pupillary diameter and calculating the actual retinal illumination (Troland). Amplitudes, being highly affected by a decrease of responding neurons due to the angle-limiting field-stop character of the pupil, cannot be matched with regard to the pupillary diameter. This effect is most noticeable in Ganzfeld illumination for the scotopic b-wave, generated mainly by neurons of the peripheral retina, and has less effect on the photopic responses that are generated more centrally.