No abstract

Affinity maturation of IgG antibodies in adaptive immune responses is a well-accepted mechanism to improve effector functions of IgG within 2 weeks to several months of antigen encounter. This concept has been defined mainly for IgG responses against chemically defined haptens. We have evaluated this concept in a viral system and analyzed neutralizing IgG antibody responses against vesicular stomatitis virus (a close relative of rabies virus) with a panel of monoclonal antibodies obtained early (day 6 or 12) and late (day 150) after hyperimmunization. These neutralizing IgG antibodies recognize a single major antigenic site with high affinities (Ka of 108-1010 litermol-1) and with rapid on-rates already on day 6 of a primary response and with no evidence for further antigen dose-and time-dependent overall improvement of affinity. This type of IgG response is probably representative for viruses or bacterial toxins which are crucially controlled by neutralizing antibodies.Studies with chemically defined small antigenic determinants-i.e., haptens-linked to a carrier protein have shown that during the immune response the late antibodies exhibit higher affinities (1) and faster on-rates (1-6) than early IgG antibodies. However, affinity maturation of an IgG antibody response taking more than a week may not be efficient enough against bacterial toxins or those cytopathic viruses where neutralizing antibodies are essential for protection, because too few antibodies may be generated too late (7-9).Vesicular stomatitis virus (VSV) is closely related to rabies virus and can infect many species; it may cause a paralytic disease after experimental peripheral infection in mice (10,11). Neutralizing IgG antibody responses specific for the viral glycoprotein of rabies virus or VSV are necessary for and efficient in protecting vertebrate hosts against infection (12-15). Interestingly, naive specific pathogen-free or conventionally kept mice generate T-cell-independent neutralizing IgM antibodies very early after infection, by day 3 or 4 (16, 17); the strictly T-cell-dependent (18) switch to IgG is observed by days 6-8. This represents a truly primary response, since VSVprimed mice exhibit an accelerated IgG response by days 2-4. High neutralizing titers of 10-4 to 10-5 are reached by days 9-12 after a primary infection and usually stay rather constant for >6 months.The present study attempted to assess the time-and dosedependent neutralizing antibody responses against VSV [substrain Indiana (Ind)]. These analyses revealed that neutralizing antibodies recognized only one major antigenic site on the viral glycoprotein. A panel of monoclonal neutralizing antibodies derived from various immunization protocols by varying time and antigen doses were used to measure and compare affinities, on-rates, and neutralizing activities. The means and ranges of these values were already high on day 6 and did notThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marke...

During most clinically relevant infections with cytopathic viruses, neutralizing antibodies are generated early, i.e., within the first week of infection. As early as 4 days after immunization of mice with vesicular stomatitis virus (VSV), a cytopathic virus closely related to rabies virus, hybridomas could be isolated that secreted virus-neutralizing IgGs. Such antibodies were devoid of somatic mutations, showed high binding avidities (approximately 10(9) M-1), and used V gene fragments predominantly belonging to the VHQ52 and VK19-28 families. In contrast, most secondary and hyperimmune response IgGs isolated 12 and 150 days after infection used several additional V gene combinations. These, which used the VHQ52/VK19-28 combination of early IgGs, were point mutated but showed only marginally enhanced binding avidities. Since all VHQ52/ VK19-28-positive IgGs bound to one subsite within the major antigenic site of VSV-G irrespective of the presence or absence of somatic point mutations, fine specificity diversification of secondary and hyperimmune responses was achieved by newly appearing V gene combinations.

In Germany, two distinct episodes of outbreaks of highly pathogenic avian influenza virus of subtype H5N1 (HPAIV H5N1) in wild birds occurred at the beginning of 2006, and in summer 2007. High local densities of wild bird populations apparently sparked clinically detectable outbreaks. However, these remained restricted in (i) number of birds, (ii) species found to be affected, (iii) time, and (iv) location despite the presence of several hundred thousands of susceptible wild birds and further stressors (food shortage, harsh weather conditions and moulting). Northern and southern subpopulations of several migratory anseriform species can be distinguished with respect to their preference for wintering grounds in Germany. This corroborates viral genetic data by Starick et al. (2008) demonstrating the introduction of two geographically restricted virus subpopulations of Qinghai-like lineage (cluster 2.2.A and 2.2.B) into northern and southern Germany, respectively, in 2006. The incursion of virus emerging in 2007, found to be distinct from the clusters detected in 2006 (Starick et al., 2008), may have been associated with moulting movements. Intensive past-outbreak investigations with negative results of live and dead wild birds and of terrestrial scavengers excluded continued circulation of virus on a larger scale. However, persistence of virus in small pockets of local wild bird populations could not be ruled out resiliently. 1.5% of investigated sera originating from cats sampled at the epicentres of the Ruegen 2006-outbreak contained H5-antibodies. Passive monitoring was found to be highly superior to live bird surveillance when aiming at the detection of HPAIV H5N1 in wild birds (P< 0.0001).