The role of BCR isotype in B-cell development and activation.

The development and function of B lymphocytes critically depend on the non-germline B-cell antigen receptor (BCR). In addition to the diverse antigen-recognition regions, whose coding sequences are generated by the somatic DNA rearrangement, the variety of the constant domains of the Heavy Chain (HC) portion contributes to the multiplicity of the BCR types. The functions of particular classes of the HC, particularly in the context of the membrane BCR, are not completely understood. The expression of the various classes of the HC correlates with the distinct stages of B-cell development, types of B-cell subsets, and their effector functions. In this chapter, we summarize and discuss the accumulated knowledge on the role of the µ, δ, and γ HC isotypes of the conventional and precursor BCR in B-cell differentiation, selection, and engagement with (auto)antigens.

Langerin+ dermal dendritic cells are critical for CD8+ T cell activation and IgH γ-1 class switching in response to gene gun vaccines.

The C-type lectin langerin/CD207 was originally discovered as a specific marker for epidermal Langerhans cells (LC). Recently, additional and distinct subsets of langerin(+) dendritic cells (DC) have been identified in lymph nodes and peripheral tissues of mice. Although the role of LC for immune activation or modulation is now being discussed controversially, other langerin(+) DC appear crucial for protective immunity in a growing set of infection and vaccination models. In knock-in mice that express the human diphtheria toxin receptor under control of the langerin promoter, injection of diphtheria toxin ablates LC for several weeks whereas other langerin(+) DC subsets are replenished within just a few days. Thus, by careful timing of diphtheria toxin injections selective states of deficiency in either LC only or all langerin(+) cells can be established. Taking advantage of this system, we found that, unlike selective LC deficiency, ablation of all langerin(+) DC abrogated the activation of IFN-γ-producing and cytolytic CD8(+) T cells after gene gun vaccination. Moreover, we identified migratory langerin(+) dermal DC as the subset that directly activated CD8(+) T cells in lymph nodes. Langerin(+) DC were also critical for IgG1 but not IgG2a Ab induction, suggesting differential polarization of CD4(+) T helper cells by langerin(+) or langerin-negative DC, respectively. In contrast, protein vaccines administered with various adjuvants induced IgG1 independently of langerin(+) DC. Taken together, these findings reflect a highly specialized division of labor between different DC subsets both with respect to Ag encounter as well as downstream processes of immune activation.

Preferential expression of human lambda-light-chain variable-region subgroups in multiple myeloma, AL amyloidosis, and Waldenström's macroglobulinemia.

We have compared the distribution of lambda-light-chain variable-region (V lambda) subgroups among Ig lambda molecules found in the serum of normal individuals with that of monoclonal Ig lambda components obtained from patients with plasma cell and related immunoproliferative disorders. A panel of monoclonal antibodies specific for each of the major human V lambda subgroups--V lambda I, V lambda II, V lambda III, V lambda IV, V lambda VI, and V lambda VIII--was used in a highly sensitive enzyme-linked immunosorbent assay (ELISA) to quantitate each of these populations. The mean distribution of Ig lambda I, Ig lambda II, Ig lambda III, Ig lambda IV, Ig lambda VI, and Ig lambda VIII molecules in serum specimens collected from 20 normal adults was approximately 40, 3, 43, 5, 5, and 3% of the total Ig lambda population, respectively. In contrast, that of monoclonal IgG, IgA, and IgD proteins and Bence Jones proteins obtained from patients with multiple myeloma and related gammopathies (n = 196) was approximately 27, 28, 39, 5, 0, and 1%, respectively. The percentage of monoclonal Ig lambda II components found in individuals with AL lambda amyloidosis (n = 41) was comparably increased to that seen in multiple myeloma and was even higher in patients with Waldenström's macroglobulinemia (n = 16), in whom 63% of the IgM lambda proteins were of the V lambda II subgroup. Also evidenced were differences in the distribution of other V lambda subgroups in the disease states: Most striking was the predominance (41%) of the V lambda VI subgroup among monoclonal lambda chains obtained from patients with AL amyloidosis and that this subgroup was found exclusively on amyloidosis-associated proteins. No Ig lambda VI-type myeloma- or macroglobulinemia-related proteins were identified. The observed alterations in V lambda subgroup distribution among "pathologic" monoclonal Igs were attributed to the particular disease and not related to the heavy-chain class. Our finding that certain V lambda subgroups are nonstochastically expressed in lambda-type multiple myeloma, AL amyloidosis, and Waldenström's macroglobulinemia provides evidence for abnormal VL gene usage in these disorders and, thus, furnishes new insight into their pathogenesis.

Class and IgG subclass distribution of antibodies against peripheral nerve myelin in sera from patients with inflammatory demyelinating polyradiculoneuropathy.

An enzyme-linked immunosorbent assay (ELISA) was used to quantify antibodies against peripheral nerve myelin (PNM) in sera from 90 patients with Guillain-Barré syndrome (GBS) and from 70 patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Fifty-nine percent of the patients with GBS and 51% of the patients with CIDP had increased levels of anti-PNM antibodies. Antibodies were also found in 0%-14% of sera from patients with other neurological diseases and in 8% of normal blood donors. Mean levels of IgG, IgM and IgA anti-PNM antibodies were increased in sera from patients with GBS, and mean IgG and IgA anti-PNM antibody levels were increased in sera from patients with CIDP when compared with sera from normal blood donors. The mean IgG anti-PNM antibody response observed in patients with GBS or CIDP was dominated by the IgG1 and IgG3 subclasses.

Class switching from gamma 3 to gamma 2b in a murine pre-B cell line.

Class switching from gamma 3 to gamma 2b production at pre-B cell stage was observed in an Abelson virus-transformed murine immature cell line that is able to perform VH to DJH recombinations followed by class switch recombinations. A series of Southern blotting experiments indicates that the class switching from gamma 3 to gamma 2b was mediated by the deletion mechanism of the intervening CH genes on the expressed chromosome and that the break points in the switch recombinations might be different from each other among six independent switching events from gamma 3 to gamma 2b. This in vitro switching system should provide us with much information on the mechanisms of class switch recombination.

Class switch recombination is IgG1 specific on active and inactive IgH loci of IgG1-secreting B-cell blasts.

Mouse B lymphocytes can be activated polyclonally by bacterial lipopolysaccharide (LPS) to secrete Ig and perform Ig class switch. In the presence of the T-cell lymphokine B-cell differentiation factor, the frequency of IgG1-secreting cells is drastically enhanced. We show here that IgG1-secreting B cells isolated from such cultures have undergone a similar DNA rearrangement of the switch regions (S mu, S gamma 1) of the Ig heavy chain constant region genes C mu and C gamma 1 on both active and inactive IgH loci. This result argues against a stochastic model of class switch recombination and suggests programmed class-specific switch recombination in the case of the switch to IgG1. In accord with this notion, cells expressing IgM but not IgG on the surface have not deleted or rearranged C mu or S gamma 1 on either chromosome.