Development of antibody-secreting cells and antigen-specific T cells in cervical lymph nodes after intranasal immunization

Intranasal (i.n.) immunization with bacterial protein antigens coupled to cholera toxin B subunit (CTB) effectively induces mucosal, especially salivary immunoglobulin A (IgA), and nonmucosal antibody responses in mice. To examine the regional distribution of antigen-specific B and T cells after i.n. immunization, antibody-secreting cells and antigen-responsive T cells in cervical lymph nodes (CLN) were compared with those found after intraoral or subcutaneous (in the neck) administration of the same antigen and with T cells found in mesenteric lymph nodes (MLN) and spleen after intragastric immunization. The i.n. immunization induced predominantly IgA antibody-secreting cells in salivary glands and IgA and IgG antibody-secreting cells in the superficial and central CLN; these responses were quantitatively enhanced if the antigen was coupled to CTB. Intraoral immunization also induced IgA and IgG antibody-secreting cells in the superficial and central CLN, but only if intact cholera toxin was included as an adjuvant. In contrast, subcutaneous (neck) immunization induced IgG antibody-secreting cells mainly in the draining facial lymph nodes. CLN cell populations resembled those of MLN, except that CLN lymphocytes had higher proportions of T cells and lower proportions of B cells and a slightly higher CD4+/CD8+ ratio among T cells than the MLN lymphocytes did. T cells that proliferated in response to antigen in vitro were found especially in central CLN 2 days after i.n. immunization and persisted for up to 6 months, whereas after intragastric immunization, responsive T cells were not found in the MLN for up to 14 days. After culture with antigen in vitro, T cells from the superficial CLN of i.n. immunized mice secreted both gamma interferon and interleukin-4. Therefore, after i.n. immunization, superficial and central CLN represent sites of regional lymphocyte development, and the central CLN in particular appear to be sites where memory T cells persist.

Induction of antibody-secreting cells and T-helper and memory cells in murine nasal lymphoid tissue

Intranasal (i.n.) immunization is an effective route for inducing mucosal immune responses especially in the upper respiratory tract and mouth. To characterize the cells involved in these responses, nasal lymphoid tissue (NALT; considered to be the equivalent of Waldeyer's ring in humans) of normal mice, and of mice immunized intranasally with a bacterial protein antigen conjugated to cholera toxin B subunit, was isolated and the lymphoid cells analysed according to surface phenotype, immunoglobulin and antibody secretion, and cytokine profile. Compared with cells obtained from Peyer's patches (PP), NALT cells contained a higher proportion of T cells, especially naive (CD45RB+hi) T-helper cells, and fewer surface (s)IgA+ cells. Both tissues contained high proportions of sIgM+ IgD+ unswitched B cells. After i.n. immunization, IgA antibody-secreting cells were increased, indicating that isotype switching and differentiation of B cells to IgA-secreting cells occurred in NALT, whereas smaller numbers of antibody-secreting cells were found in PP after intragastric (i.g.) immunization. Antigen-specific memory cells persisted in NALT for at least 8 months after initial immunization. The cytokine expression profiles of antigen-stimulated NALT and PP cells of immunized mice, revealed by reverse transcription polymerase chain reaction analysis of mRNA, were similar. Both NALT and PP cells tended to express type 2 earlier or for longer than type 1 cytokine mRNA, but NALT cells tended to express interleukin-4 (IL-4) earlier, and IL-5 for a longer period, than PP cells. Thus NALT shares with PP cell populations typical of a mucosal inductive site, including unswitched B cells and naive T-helper (Th) cells. After i.n. immunization, NALT has the capacity to provide help for B-cell maturation and differentiation, as well as to maintain immune memory.

Dual function of human IgA antibodies: inhibition of phagocytosis in circulating neutrophils and enhancement of responses in IL-8-stimulated cells

We have sought to elucidate the responses of human peripheral blood neutrophils to antigenic surfaces complexed with human specific IgA antibodies obtained either as myeloma proteins that recognize staphylococcal alpha-toxin, or from the serum of patients with subacute bacterial endocarditis due to Streptococcus mutans, or from colostrum. In contrast to IgG, IgA antibodies bound to antigen-coated fluorescent microspheres, and subsequently exposed to complement (or not), did not promote phagocytosis, as measured by flow cytometric enumeration of cell-associated microspheres. Instead, IgA antibodies interfered with complement-dependent phagocytosis mediated by IgG antibodies. These properties were shown by different forms of IgA antibodies, including serum and secretory IgA, as well as by monoclonal or polyclonal antibodies. Neutrophils did not respond to the production of superoxide to IgA antibodies complexed with antigen-coated microspheres or with antigen deposited on a solid surface and IgA antibodies suppressed IgG antibody- and complement-mediated superoxide release. However, neutrophils pretreated with interleukin-8 ingested IgA-opsonized microspheres and released superoxide when exposed to IgA antibody-antigen complexes. IgG antibody-antigen complexes did not stimulate increased superoxide release in interleukin-8-treated neutrophils. These findings were consistent with a selective increase in the surface expression of Fc alpha R by interleukin-8-treated neutrophils. We conclude that IgA antibodies interfere with the phagocytic activities of normal circulating human neutrophils and may promote these activities in inflammatory neutrophils activated by interleukin-8 in which Fc alpha R is up-regulated.

The role of the carbohydrate chains in complement (C3) fixation by solid-phase-bound human IgA

In contrast to antigen-antibody complexes containing native human IgA, solid-phase-deposited IgA activates the alternative complement pathway and binds C3b. To investigate the role of carbohydrate chains in this, various human IgA preparations were treated with neuraminidase alone or together with N-glycanase or O-glycanase, or with mixed glycosidases from the oral bacterium, Streptococcus mitis. Depletion of oligosaccharides was determined by carbohydrate analysis. Removal of sialic acid and N-linked glycan chains greatly increased the C3b-fixing properties of normal serum IgA1 and IgA2. Myeloma IgA1 and IgA2 proteins and secretory IgA had higher C3b-binding activity than normal serum IgA, and this was further increased by removal of sialic acid and N-linked glycans. Fc alpha and Fc alpha-SC fragments of myeloma and secretory IgA1, respectively, but not Fab alpha fragments, obtained by cleavage with bacterial IgA1 proteases and also free secretory component, fixed C3b by the alternative pathway.

All forms of human IgA antibodies bound to antigen interfere with complement (C3) fixation induced by IgG or by antigen alone

Polyclonal human secretory IgA1 and IgA2 antibodies to a bacterial protein antigen Streptococcus mutans AgI/II, and polyclonal human serum IgA1 and IgA2 antibodies to staphylococcal alpha-toxin, were found to interfere with antigen-mediated C3b fixation. In fluid phase, immune complexes of antigen and IgA failed to fix C3b, whereas antigen-IgG complexes did fix C3b. Partial removal of glycan chains with Streptococcus mitis SK96 glycosidases diminished the capacity of IgA antibodies to interfere with antigen-mediated C3b fixation by the alternative complement pathway. The authors conclude that native serum or secretory IgA antibodies suppress C3b fixation, and that the glycan chains play a significant role in maintaining this property.