Characterization of a natural mutation in an antigenic site on the fusion protein of measles virus that is involved in neutralization.

Although measles virus is an antigenically monotypic virus, nucleotide sequence analysis of the hemagglutinin and nucleoprotein genes has permitted the differentiation of a number of genotypes. In contrast, the fusion (F) protein is highly conserved; only three amino acid changes have been reported over a 40-year period. We have isolated a measles virus strain which did not react with an anti-F monoclonal antibody (MAb) which we had previously shown to be directed against a dominant antigenic site. This virus strain, Lys-1, had seven amino acid changes compared with the Edmonston strain. We have shown that a single amino acid at position 73 is responsible for its nonreactivity with the anti-F MAb. With the same MAb, antibody-resistant mutants were prepared from the vaccine strain. A single amino acid change at position 73 (R-->W) was observed. The possibility of selecting measles virus variants in vaccinated populations is discussed.

Canine distemper virus DNA vaccination induces humoral and cellular immunity and protects against a lethal intracerebral challenge.

We have studied the immune responses to the two glycoproteins of the Morbillivirus canine distemper virus (CDV) after DNA vaccination of BALB/c mice. The plasmids coding for both CDV hemagglutinin (H) and fusion protein (F) induce high levels of antibodies which persist for more than 6 months. Intramuscular inoculation of the CDV DNA induces a predominantly immunoglobulin G2a (IgG2a) response (Th1 response), whereas gene gun immunization with CDV H evokes exclusively an IgG1 response (Th2 response). In contrast, the CDV F gene elicited a mixed, IgG1 and IgG2a response. Mice vaccinated (by gene gun) with either the CDV H or F DNA showed a class I-restricted cytotoxic lymphocyte response. Immunized mice challenged intracerebrally with a lethal dose of a neurovirulent strain of CDV were protected. However, approximately 30% of the mice vaccinated with the CDV F DNA became obese in the first 2 months following the challenge. This was not correlated with the serum antibody levels.

Immunization with plasmid DNA encoding for the measles virus hemagglutinin and nucleoprotein leads to humoral and cell-mediated immunity.

We have evaluated the DNA vaccination strategy for measles virus (MV) hemagglutinin (HA) and nucleoprotein (NP) genes. Plasmids encoding either the MV, HA, or NP proteins inoculated intramuscularly into Balb/c mice induced both humoral and CTL class I restricted responses. Antibody responses were not increased by multiple inoculations. The major antibody isotype induced by both the HA and NP was IgG2a consistent with a Th1 response. In contrast, immunization with a plasmid which directed the synthesis of a partially secreted form of HA gave mainly IgG1 antibodies. When the amount of DNA was reduced for the HA plasmid (1 or 10 microg/animal), although the antibody was not induced, a CTL response was observed.

Measles virus fusion: role of the cysteine-rich region of the fusion glycoprotein.

Measles virus (MV) fusion requires the participation of both the fusion (F) and hemagglutinin (H) glycoproteins. The canine distemper virus fusion protein (CDVF) cannot substitute for the measles virus fusion protein (MVF) in this process. Introduction of restriction enzyme sites into the cDNAs of CDVF and MVF by site-directed mutagenesis facilitated the production of chimeric F proteins which were tested for their capacity to give fusion when coexpressed with MVH. Fusion resulted when the amino-terminal half of the MVF cysteine-rich region was transferred to CDVF.

Effects of atrial pacing on right ventricular contractility after coronary artery surgery.

Increasing heart rate enhances the strength of contraction of cardiac fibers. This has been demonstrated in vitro and recently for the left ventricle. To study this phenomenon on the right ventricle, the effects of increasing heart rate by atrial pacing on right ventricular (RV) contractility were observed after coronary artery surgery in 20 patients. Right ventricular ejection fraction (EF) and stroke volume (SV) were measured by use of a rapid-response thermistor pulmonary artery catheter. Right ventricular volumes were calculated from EF and SV. Right ventricular contractility was assessed by the slope of the end-systolic pressure-volume relationship (ESPVR) before and after increasing RV preload by means of military antishock trousers (MAST) inflation. The dP/dtmax/end-diastolic volume index (EDVI) ratio, which is independent of ventricular preload, was also used as an inotropic index. Results are expressed as mean +/- SEM. Right ventricular preload, as reflected by RVEDVI, was increased by MAST inflation (99 +/- 6 mL/m2 v 106 +/- 7 mL/m2, P < 0.01), but returned to control values when inflation of MAST was combined with pacing (100 +/- 6 mL/m2). The slope of the RV ESPVR significantly increased when heart rate was increased (0.22 +/- 0.03 mmHg/mL/m2 before pacing v 0.77 +/- 0.07 mmHg/mL/m2 during pacing, P < 0.05). The dP/dtmax/EDVI ratio was also increased by pacing (2.32 +/- 0.4 mmHg/min/mL/m2 before pacing v 3.15 +/- 0.5 mmHg/min/mL/m2 during pacing, P < 0.01). Moreover, cardiac index was increased by pacing alone (2.45 +/- 0.2 L/min/m2 v 2.78 +/- 0.2 L/min/m2, P < 0.01), and significantly more when MAST were inflated (2.94 +/- 0.2 mL/m2, P < 0.05 v pacing alone). It is concluded that increasing heart rate by atrial pacing increases RV inotropic status after coronary artery surgery.