In vitro regulation of IgA subclass synthesis. I. Discordance between plasma cell production and antibody secretion.

Abstract

In all normal individuals, the IgA in the serum and secretions can be divided into two subclasses, IgAa and IgA~, on the basis of antigenic differences. IgAa constitutes 80-90% of the IgA in serum (1-3), whereas approximately equal amounts of IgA1 and IgA2 occur in the secretions (2).Our previous studies have shown that although the IgA B cell distribution in the peripheral circulation reflects serum ratios of IgAa to IgA2, that is, 80% of the cells express surface IgA1 and 20% bear IgA2 (4), the differentiation potential of peripheral blood lymphocytes in response to polyclonal B cell activators is quite different and more closely resembles the distribution of IgAx and IgA2 in secretions. In cultures stimulated with pokeweed mitogen (PWM) for 7 d, 50% of the plasma ceils that are positive for cytoplasmic IgA are positive for IgA1 and 50% are positive for IgA2 (4). This suggests that the cells in the circulation that differentiate into IgA plasma cells in response to PWM may be cells migrating to the mucosal surfaces. The observation that most of the IgA released into the supernatants of these cultures is dimeric, like IgA in secretions, rather than monomeric, like serum IgA (5), supports this hypothesis.To further investigate regulation of IgA subclasses in PWM-stimulated cultures, IgA1 and IgA2 were measured in culture supernatants by a radioimmunoassay we have recently devised using monoclonal anti-IgA subclass antibodies (3). The results demonstrate that although there are equal numbers of IgA1 and IgA2 plasma cells in PWM-stimulated cultures, >90% of the IgA released into the culture supernatant is IgA1. This discrepancy cannot be accounted for by failure of the assay to detect in vitro synthesized IgA2, selective loss or destruction of IgA2, delayed release of IgA2, or failure of IgA2 plasma cells to produce J chain.Materials and Methods PWM Cultures. Peripheral blood lymphocytes from healthy adult laboratory personnel were separated from heparinized venous blood by Ficoll-Hypaque centrifugation. The cells were suspended in RPMI 1640 (Gibco Laboratories, Grand Island Biological Co., Grand Island, NY) with 20% fetal calf serum (FCS) at 5-10 × 106 cells/ml and incubated in plastic petri dishes at 37 ° for 45 min to partially deplete monocytes. Nonadherent lymphocytes were resuspended in RPMI 1640 with 2 mM glutamine, 100 U/ml penicillin, 100 mg/ml streptomycin, 0.05 mM 2 mercaptoethanol, and 20% FCS at a concentration of 106 cells/ml. Aliquots

The Mucosal B Cell System

“…This is in accordance with the observed intestinal adaptation in relation to bacterial exposure, with increased IgA2 and decreased IgM production by lamina propria PCs (Kett et al, 1995). Sequential switching from IgA1 to IgA2 was observed neither in the colon (Lin et al, 2014) nor in pokeweed mitogen-stimulated peripheral blood lymphocytes (Conley and Bartelt, 1984).…”

Charge Distribution of IgA-Lambda in IgA Nephropathy

“…IgA synthesized by these circulating B lymphocytes express properties of IgA secreted by muco sal-associated lymphoid tissue with a predominant produc tion of polymeric IgA [22] and an equal proportion of IgA 1 and IgA2 [23]. We had previously demonstrated that the percentage of IgA 1 in serum and the k/A ratio of serum IgA 1 were unchanged during clinical exacerbation in pa tients with IgA nephropathy [10].…”

Selective deficiency of immunoglobulin A2.

“…IgA-bearing cells were present in all family members studied (Table IV) (Table IV); mother (I-2) and daughter (II-2) showed only IgAl-containing blasts. In contrast, the plasmablasts of II-3 included IgAl-as well as IgA2-containing cells in a ratio as previously described (22,25 (6).…”