Immunoglobulin switch transcript production in vivo related to the site and time of antigen-specific B cell activation.

Abstract

SummaryImmunoglobulin (Ig) class switch recombination is associated with the production and splicing of germline IgCH messenger RNA transcripts. Levels of'y1 transcripts in mouse spleen sections were assessed by semiquantitative analysis of reverse transcriptase polymerase chain reaction (PCk) products during primary and secondary antibody responses to chicken gamma globulin (CGG). This was correlated with the appearance of CGG-specific B cells and their growth and differentiation to plasma cells. After primary immunization with CGG, ~/1 switch transcripts appeared after 4 d, peaked at a median of six times starting levels between 10 and 18 d after immunization, and returned to background levels before secondary immunization at 5 wk. By contrast, after secondary challenge with CGG, a sevenfold increase in transcripts occurs during the first d. The level again doubles by day 3, when it is six times that which is seen at the peak of the primary response. After day 4, there was a gradual decline over the next 2-3 wk. Within 12 h of secondary immunization, antigen-specific memory B cells appeared in the outer T zone and by 24 h entered S phase, presumably as a result of cognate interaction with primed T cells. Over the next few hours, they migrated to the edge of the red pulp, where they grew exponentially until the fourth day, when they synchronously differentiated to become plasma cells. The same pattern was seen for the migration, growth, and differentiation of virgin hapten-specific B cells when CGG-primed mice were challenged with hapten protein. The continued production of transcripts after day 3 indicates that switching also occurs in germinal centers, but in a relatively small proportion of their B cells. The impressive early production of switch transcripts during T cell-dependent antibody responses occurs in cells that are about to undergo massive clonal expansion. It is argued that Ig class switching at this time, which is associated with cognate T cell-B cell interaction in the T zone, has a major impact on the class and subclasses of Ig produced during the response.

Recirculating CD4 memory T cells mount rapid secondary responses without major contributions from follicular CD4 effectors and B cells

“…This was assessed by the rate of induction of synthesis of IL-4 mRNA, which in responses of this sort of antigen is produced by antigen-specific CD4 T cells [26]. Further, B cell-derived IgG H chain germ-line transcripts were detected as markers for CD4 T celldependent B cell activation [15,27].…”

“…Protein antigens CGG, NP-CGG, and PCC (Sigma-Aldrich, Poole, UK) were prepared as described [15,16]. Primary immunization was done with 25 lg alum-precipitated protein per 20 lL saline.…”

“…Immunohistology was performed as described previously [1,15,16]. An additional antibody used was rabbit anti-mouse Ki-67 antiserum (gift from Johannes Gerdes, Borstel, Germany) labeled with swine anti-rabbit Ig antiserum (Dako, Glostrup, Denmark), followed by rabbit PAP (Dako).…”

“…An additional antibody used was rabbit anti-mouse Ki-67 antiserum (gift from Johannes Gerdes, Borstel, Germany) labeled with swine anti-rabbit Ig antiserum (Dako, Glostrup, Denmark), followed by rabbit PAP (Dako). Sections were developed as described [15].…”

“…In lymphoid tissues, CD4 memory T cells and B cells interact in the outer T zone within hours of secondary immunization [15]. It is unclear whether the responding CD4 T cell in this situation is a central memory T cell [16,17], or whether effector T cells, like the T cells that colonize follicles in LN responding to antigen, play a major role.…”