Identification of a streptococcal octapeptide motif involved in acute rheumatic fever

Acute rheumatic fever is a serious autoimmune sequela of pharyngitis caused by certain group A streptococci. One mechanism applied by streptococcal strains capable of causing acute rheumatic fever is formation of an autoantigenic complex with human collagen IV. In some geographic regions with a high incidence of acute rheumatic fever pharyngeal carriage of group C and group G streptococci prevails. Examination of such strains revealed the presence of M-like surface proteins that bind human collagen. Using a peptide array and recombinant proteins with targeted amino acid substitutions, we could demonstrate that formation of collagen complexes during streptococcal infections depends on an octapeptide motif, which is present in collagen binding M and M-like proteins of different beta-hemolytic streptococcal species. Mice immunized with streptococcal proteins that contain the collagen binding octapeptide motif developed high serum titers of anti-collagen antibodies. In sera of rheumatic fever patients such a collagen autoimmune response was accompanied by specific reactivity against the collagen-binding proteins, linking the observed effect to clinical cases. Taken together, the data demonstrate that the identified octapeptide motif through its action on collagen plays a crucial role in the pathogenesis of rheumatic fever. Eradication of streptococci that express proteins with the collagen binding motif appears advisable for controlling rheumatic fever.     

Group G streptococcal IgG binding molecules FOG and protein G have different impacts on opsonization by C1q

Recent epidemiological data on diseases caused by beta-hemolytic streptococci belonging to Lancefield group C and G (GCS, GGS) underline that they are an emerging threat to human health. Among various virulence factors expressed by GCS and GGS isolates from human infections, M and M-like proteins are considered important because of their anti-phagocytic activity. In addition, protein G has been implicated in the accumulation of IgG on the bacterial surface through non-immune binding. The function of this interaction, however, is still unknown. Using isogenic mutants lacking protein G or the M-like protein FOG (group G streptococci), respectively, we could show that FOG contributes substantially to IgG binding. A detailed characterization of the interaction between IgG and FOG revealed its ability to bind the Fc region of human IgG and its binding to the subclasses IgG1, IgG2, and IgG4. FOG was also found to bind IgG of several animal species. Surface plasmon resonance measurements indicate a high affinity to human IgG with a dissociation constant of 2.4 pm. The binding site was localized in a central motif of FOG. It has long been speculated about anti-opsonic functions of streptococcal Fc-binding proteins. The presented data for the first time provide evidence and, furthermore, indicate functional differences between protein G and FOG. By obstructing the interaction between IgG and C1q, protein G prevented recognition by the classical pathway of the complement system. In contrast, IgG that was bound to FOG remained capable of binding C1q, an effect that may have important consequences in the pathogenesis of GGS infections.     

Role of APOBEC3 in genetic diversity among endogenous murine leukemia viruses

The ability of human and murine APOBECs (specifically, APOBEC3) to inhibit infecting retroviruses and retrotransposition of some mobile elements is becoming established. Less clear is the effect that they have had on the establishment of the endogenous proviruses resident in the human and mouse genomes. We used the mouse genome sequence to study diversity and genetic traits of nonecotropic murine leukemia viruses (polytropic [Pmv], modified polytropic [Mpmv], and xenotropic [Xmv] subgroups), the best-characterized large set of recently integrated proviruses. We identified 49 proviruses. In phylogenetic analyses, Pmvs and Mpmvs were monophyletic, whereas Xmvs were divided into several clades, implying a greater number of replication cycles between the integration events. Four distinct primer binding site types (Pro, Gln1, Gln2 and Thr) were dispersed within the phylogeny, indicating frequent mispriming. We analyzed the frequency and context of G-to-A mutations for the role of mA3 in formation of these proviruses. In the Pmv and Mpmv (but not Xmv) groups, mutations attributable to mA3 constituted a large fraction of the total. A significant number of nonsense mutations suggests the absence of purifying selection following mutation. A strong bias of G-to-A relative to C-to-T changes was seen, implying a strand specificity that can only have occurred prior to integration. The optimal sequence context of G-to-A mutations, TTC, was consistent with mA3. At least in the Pmv group, a significant 5′ to 3′ gradient of G-to-A mutations was consistent with mA3 editing. Altogether, our results for the first time suggest mA3 editing immediately preceding the integration event that led to retroviral endogenization, contributing to inactivation of infectivity.     

The evolution of partial migration in Birds

Partial migration, i.e.when one fraction of the population is migratory and the other sedentary, appears to be a widespread phenomenon among many animal taxa, ranging from insects to higher vertebrates. Partial migration in birds was first documented for several Holarctic populations many decades ago. The evolution and maintenance of this particular migratory system have only recently been more thoroughly examined, but our knowledge and understanding of the problem is still incomplete. Currently, one of the main concerns is the fitness balancing of the two behavioural alternatives, i.e. whether migrants and residents within a population are equally fit or if one of the categories is inferior and making 'the best of a bad situation'. Closely tied to this question is the proximate regulation of the migratory and sedentary habits. It has been suggested that a social dominance system might be powerful enough to keep this migration system going; alternatively, a pooulation might be divided into two genetically distinct morphs with different preprogrammed Migratory behaviours.     

Dispersal, migration, and offspring retention in saturated habitats

We examine the evolutionary stability of year-round residency in territorial populations, where breeding sites are a limiting resource. The model links individual life histories to the population-wide competition for territories and includes spatial variation in habitat quality as well as a potential parent-offspring conflict over territory ownership. The general form of the model makes it applicable to the evolution of dispersal, migration, partial migration, and delayed dispersal (offspring retention). We show that migration can be evolutionarily stable only if year-round residency in a given area would produce a sink population, where mortality exceeds reproduction. If this applies to a fraction of the breeding habitat only, partial migration is expected to evolve. In the context of delayed dispersal, habitat saturation has been argued to form an ecological constraint on independent breeding, which favors offspring retention and cooperative breeding. We show that habitat saturation must be considered as a dynamic outcome of birth, death, and dispersal rates in the population, rather than an externally determined constraint. Although delayed dispersal often associates with intense competition for territories, life-history traits have direct effects on stable dispersal strategies, which can often override the effect of habitat saturation. As an example, high survival of floaters selects against delayed dispersal, even though it increases the number of competitors for each breeding vacancy (the "habitat saturation factor"). High survival of territory owners, by contrast, generally favors natal philopatry. We also conclude that spatial variation in habitat quality only rarely selects for delayed dispersal. Within a population, however, offspring retention is more likely in high-quality territories.     

Gender influences herpes simplex virus type 1 infection in normal and gamma interferon-mutant mice

Gender influences the incidence and severity of some bacterial and viral infections and autoimmune diseases in animal models and humans. To determine a gender-based difference, comparisons were made between male and female mice inoculated with herpes simplex virus type 1 (HSV-1) by the corneal route. Mortality was higher in the male mice of the three strains tested: 129/Sv//Ev wild type, gamma interferon (IFN-gamma) knockout (GKO), and IFN-gamma receptor knockout (RGKO). Similarly, in vivo HSV-1 reactivation occurred more commonly in male mice, but the male-female difference in reactivation was restricted to the two knockout strains and was not seen in the 129/Sv//Ev control. Comparison among male mice of the three strains showed a higher mortality of the RGKO mice and a higher reactivation rate of the GKO and RGKO mice than of the 129/Sv//Ev males. In contrast, female RGKO and GKO mice did not differ from female 129/Sv//Ev controls in either mortality or reactivation. HSV-1 periocular and eyelid disease was also more severe in male and dihydrotestosterone (DHT)-treated female mice than in control female mice. These results show a consistent gender difference in HSV-1 infection, with a worse outcome in male mice. In addition, the results comparing GKO and RGKO mice to controls show differences only in male mice, suggesting that some effects of IFN-gamma, a key immunoregulatory molecule, are gender specific.