Transcriptional control of activation-induced cytidine deaminase and error-prone DNA polymerases is functionally mature in the B cells of infants at birth.

Somatic hypermutation (SHM) of immunoglobulin genes requires activation-induced cytidine deaminase (AID). The error-prone DNA polymerases, such as Pol eta, Pol zeta, and Pol iota, also have been implicated in the process. Human adult antibodies directed to microbial pathogens are increased in affinity and function compared with those of infants. Adult antibodies achieve this increased affinity through somatic mutations, which are lacking in the B cells of infants. It is unknown if infant B cells are capable of upregulating the cell machinery needed to introduce mutations after stimulation through the antigen receptor. We show here that infant B cells exhibit similar kinetics and magnitude of transcription of AID and pol eta genes and only marginally lower levels of pol iota and pol zeta genes after stimulation through the B cell receptor. These data suggest that the ability to upregulate gene transcription of enzymes mediating SHM is not a limiting determinant of the functional quality of infant antibody responses.

VH1-46 is the dominant immunoglobulin heavy chain gene segment in rotavirus-specific memory B cells expressing the intestinal homing receptor alpha4beta7.

Memory B cells expressing the intestinal homing marker alpha4beta7 are important for protective immunity against human rotavirus (RV). It is not known whether the B cell repertoire of intestinal homing B cells differs from B cells of the systemic compartment. In this study, we analyzed the RV-specific VH and VL repertoire in human IgD- B cells expressing the intestinal homing marker alpha4beta7. The mean frequency of RV-specific B cells in the systemic compartment of healthy adult subjects was 0.6% (range, 0.2-1.2). The mean frequency of IgD- B cells that were both RV specific and alpha4beta7 was 0.04% (range, 0.01-0.1), and a mean of 10% (range, 1-32) of RV-specific peripheral blood human B cells exhibited an intestinal homing phenotype. We previously demonstrated that VH1-46 is the dominant Ab H chain gene segment in RV-specific systemic B cells from adults and infants. RV-specific systemic IgD- or intestinal homing IgD-/alpha4beta7+ B cells in the current study also used the gene segment VH1-46 at a high frequency, while randomly selected B cells with those phenotypes did not. These data show that VH1-46 is the immunodominant gene segment in human RV-specific effector B cells in both the systemic compartment and in intestinal homing lymphocytes. The mean replacement/silent mutation ratio of systemic compartment IgD- B cells was >2, consistent with a memory phenotype and antigenic selection. Interestingly, RV-specific intestinal homing IgD-/alpha4beta7+ B cells using the VH1-46 gene segment were not mutated, in contrast to systemic RV-specific IgD- B cells.

Cooperativity of actin and microtubule elements during replication of respiratory syncytial virus.

Many paramyxoviruses appear to require cytoskeletal elements for particular steps in the virus life cycle. Measles virus and Sendai virus exhibit a requirement for microtubules in replication in vitro, whereas parainfluenza virus type 3 and RSV require actin for replication. To further elucidate the role of cytoskeletal function and rearrangement in the viral life cycle of RSV, we investigated the efficiency of virus entry, transcription, replication, and budding in the presence of a variety of pharmacological agents that stabilize or depolymerize actin or microtubules. We found that alteration of microtubule or actin function resulted in blocks at entry, formation of cell-associated virus, virus release, local cell-to-cell spread, and syncytium formation. Actin and microtubules act in cooperation to facilitate replication of RSV, although microtubules play a dominant role in the formation of cell-associated virus while actin plays a more prominent role in virus release.