Pattern of functional antibody activity against Haemophilus influenzae type b (Hib) in infants immunized with diphtheria-tetanus-pertussis/Hib Brazilian combination vaccine

We evaluated the functional activity of Haemophilus influenzae B (Hib) antibodies elicited in a group of infants immunized with the diphtheria-tetanus-pertussis vaccine combined with an Hib vaccine produced totally in Brazil after technological transfer of Hib vaccine production from Glaxo SmithKline, Belgium. Blood samples from immunized infants (N = 985) were collected for the determination of Hib antibodies. Total Ig and IgM and IgG subclasses of antibodies against polyribosyl ribitol phosphate (PRP) were analyzed by ELISA. Almost all vaccinees (97.56 percent, 961/985) developed a strong anti-PRP IgG antibody response (¡Ý1.0 ¦Ìg/mL), while an anti-PRP IgM response was observed in 64.24 percent (634/985) of them (¡Ý0.15 ¦Ìg/mL). Only 18.88 percent (186/985) of the infants in the group with high PRP antibody IgG concentrations (¡Ý1.0 ¦Ìg/mL) developed a high IgM antibody response. Anti-PRP IgG antibody levels were significantly higher than anti-PRP IgM. These results demonstrate the predominance of IgG antibodies over IgM antibodies in response to PRP, with a ratio of 17:1. IgG antibodies were predominantly of the IgG1 subclass. An increase in IgG avidity was also observed during the course of immunization.

Relationship between apoptosis and thymocyte depletion in rabies-infected mice

The apoptosis of thymocytes from rabies-infected mice was investigated in a kinetic study covering the entire course of the infection. For this study, BALB/c mice (6-7-week old females) were inoculated intracerebrally with 100 LD50 of Challenge Virus Strain, a fixed rabies virus strain, and three animals were sacrificed per time point to remove thymuses. When thymocytes were fixed, stained with propidium iodide and analyzed by flow cytometry, a distinct subpopulation of cells was observed below the G0/G1 region, denoted as the A0 region. Cells in this region presented reduced fluorescence, and nuclear DNA fragmentation. The accumulation of cells in the A0 region, after infection, progressively increased, reaching 12 for unfractionated thymocytes, 62 for thymocytes from the 60 Percoll interface and 32 for thymocytes recovered at the 100 Percoll interface. This finding, observed only in thymocytes from infected mice, demonstrates a clear modification of chromatin condensation in these cells, suggesting the occurrence of an apoptotic process during rabies infection.