Lymphocyte activation by the Fc region of immunoglobulins

Plasma cell infiltration and treatment effect in breast cancer patients treated with neoadjuvant chemotherapy

Background

Tumour-infiltrating lymphocyte (TIL)-high breast tumours have a high rate of pathological complete response (pCR) with neoadjuvant chemotherapy. In our routine pathological diagnoses of biopsy specimens from pCR cases, we have observed a high infiltration of plasma cells (PCs). A positive correlation of PCs with favourable patient outcome has recently been reported, but little is known about how PCs contribute to local tumour immunity.

Methods

We retrospectively examined biopsy specimens from 146 patients with invasive breast cancer who received neoadjuvant chemotherapy. CD138⁺ PC infiltration was assessed by immunohistochemistry. Multiplexed fluorescent immunohistochemistry (mfIHC) with T and B cell markers was also conducted to elucidate the profile of immune cells.

Results

Greater PC infiltration was observed in the pCR group (p = 0.028) and this trend was confirmed in another patient cohort. With mfIHC, we observed significantly more CD8⁺, T-bet⁺CD4⁺, and CD8⁺FOXP3⁺ T cells, total B cells and PCs in pCR cases. Such cases were also characterised by high expression of both PD-1 and PD-L1 on B cells and PCs. In patients with hormone receptor-negative tumours, high PC infiltration was correlated with significantly longer disease-free survival (p = 0.034).

Conclusions

We found that higher PC infiltration in biopsy specimens before neoadjuvant chemotherapy was associated with pCR. With mfIHC, we also revealed that the local cytotoxic immune response was clearly enhanced in pCR cases, as was the infiltration of B cells including PCs. Moreover, higher PC levels were correlated with favourable outcomes in hormone receptor-negative breast cancer patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01477-w.

Structure of the murine unglycosylated IgG1 Fc fragment

A prototypic IgG antibody can be divided into two major structural units: the antigen-binding fragment (Fab) and the Fc fragment that mediates effector functions. The IgG Fc fragment is a homodimer of the two C-terminal domains (C(H)2 and C(H)3) of the heavy chains. Characteristic of the Fc part is the presence of a sugar moiety at the inner face of the C(H)2 domains. The structure of this complex branched oligosaccharide is generally resolved in crystal structures of Fc fragments due to numerous well-defined sugar-protein interactions and a small number of sugar-sugar interactions. This suggested that sugars play an important role in the structure of the Fc fragment. To address this question directly, we determined the crystal structure of the unglycosylated Fc fragment of the murine IgG1 MAK33. The structures of the C(H)3 domains of the unglycosylated Fc fragment superimpose perfectly with the structure of the isolated MAK33 C(H)3 domain. The unglycosylated C(H)2 domains, in contrast, approach each other much more closely compared to known structures of partly deglycosylated Fc fragments with rigid-body motions between 10 and 14 A, leading to a strongly "closed" conformation of the unglycosylated Fc fragment. The glycosylation sites in the C'E loop and the BC and FG loops are well defined in the unglycosylated C(H)2 domain, however, with increased mobility and with a significant displacement of about 4.9 A for the unglycosylated Asn residue compared to the glycosylated structure. Thus, glycosylation both stabilizes the C'E-loop conformation within the C(H)2 domain and also helps to ensure an "open" conformation, as seen upon Fc receptor binding. These structural data provide a rationale for the observation that deglycosylation of antibodies often compromises their ability to bind and activate Fcgamma receptors.

Salivary IgA subclasses and bacteria-reactive IgA in patients with aggressive periodontitis

The local salivary immunoglobulin A (IgA) response in patients with aggressive periodontitis to oral microorganisms and its role for the pathogenesis has not been determined. This study investigated the hypothesis that aggressive periodontitis patients have impaired oral secretory immunity. Our test group was made-up of 19 aggressive periodontitis patients and 19 age- and gender-matched periodontally healthy controls. Total IgA, IgA subclass 1, IgA subclass 2 and IgA reactive to Actinobacillus actinomycetemcomitans Y4, Treponema denticola ATCC 35404 and Candida albicans DSM 3454 were determined by enzyme-linked immunosorbent assay in whole unstimulated and stimulated saliva. A statistically significantly lower concentration and secretion rate of total salivary IgA (P < 0.01) and IgA1 (P < 0.001) was found in the aggressive periodontitis group in resting and stimulated saliva. A decrease of IgA2 (P < 0.05) was seen in resting saliva. Although only minor differences were detected in the concentration and secretion of bacteria-reactive IgA in both groups, the proportion of bacteria-reactive IgA from the total IgA was significantly higher (P < 0.01) in the aggressive periodontitis group in all three microorganisms tested. Our results indicate an inhibition of total secretory IgA. In particular an IgA subclass 1-specific decrease in aggressive periodontitis was noted, while the bacteria-reactive humoral immune system in saliva was activated. The role of the decrease of IgA1 immunoglobulins in aggressive periodontitis with respect to susceptibility for periodontal diseases has to be elucidated.

Modulatory effect of synthetic human IgG Fc peptides on the in vitro immune response of murine spleen cells

Synthetic peptides representative of defined surface-exposed sequences within the CH-2 and CH-3 domains of human IgG1 induce IgM production by murine spleen cells, even in cultures depleted of T-lymphocytes. This stimulation was not altered by simultaneous administration of dextran sulphate in suboptimal concentration, its effect being additive to that of the peptides. Cell proliferation was augmented only at 10(-4) M doses of peptides. IL-1 production by adherent cells was also increased as a result of peptide treatment; whilst administration of exogenous IL-1, 4 h later, seemed to abrogate the effect of peptide treatment on the augmentation of IgM production. Peptide treatment failed to induce IL-2 and/or IL-4 production. The effect of IgG peptides seems to be exerted directly on B-cells at an early step of activation and to be mediated at least in part by IL-1.

Aggregated immunoglobulin and Fc fragment of IgG induce IL-6 release from human monocytes

The Fc fragment of immunoglobulin (Ig) has been shown to play an important role in the regulation of humoral immunity, cellular immunity, lymphocyte and monocyte activation, and immune mediator secretion. We wished to determine if Ig or Fc fragments would induce IL-6 production from monocytes. Incubation of monocytes purified from human peripheral blood mononuclear cells with aggregated Ig or Fc fragments of Ig induced interleukin-6 (IL-6) activity in the supernatants. Monomeric Ig taken from an intravenous preparation of Ig, from which all aggregated Ig are removed, would not induce IL-6 production from monocytes whereas as a heat-treated aliquot, presumably containing aggregates, did induce IL-6. The supernatants were assayed according to their ability to induce growth in a murine hybridoma cell line B9, or enhance Ig secretion of B cells stimulated with Staphylococcus aureus Cowan 1 (SAC). The IL-6 activity in the supernatants could be neutralized by a polyclonal rabbit anti-human IL-6 antiserum in both assays of IL-6 activity. Exposure of T-enriched or B-enriched lymphocyte subpopulations to Fc fragments did not induce the release of any IL-6 after 12 hr of incubation, but small amounts of IL-6 were produced by B-enriched cells after 60 hr of exposure to Fc fragments. Hence Fc fragments and aggregated Ig induce peripheral blood monocytes to rapidly secrete large quantities of interleukin-6.

Lymphocyte proliferative response to mitogenic monoclonal antibodies in systemic sclerosis. Evidence for unresponsiveness to murine monoclonal antibodies of IgG1 isotype

Proliferative response of peripheral blood mononuclear cells to phitohemoagglutinin and anti-CD3 mitogenic monoclonal antibodies (MoAbs) of the IgG2a (OKT3) and IgG1 (PanT2, CLB T3/4.1) isotypes was studied in 39 patients with systemic sclerosis (SSc) and in 82 control subjects. The effect of IL-2 on this response was also investigated. No difference in the response to PHA and to IgG2a anti-CD3 MoAb OKT3 was seen between scleroderma patients and controls. Both the patient and control groups contained responders and non-responders to IgG1 anti-CD3 MoAbs. The percentage of non-responders was significantly higher in scleroderma patients than in controls. When purified lymphocytes from non-responder scleroderma patients were cultured with monocytes from control responders, proliferative response to IgG1 MoAbs was restored. Our results show that monocytes from patients with systemic sclerosis bear a defect leading to IgG1 unresponsiveness by T lymphocytes.

Distribution of immunoglobulin isotypes including IgA subclasses in adult, juvenile, and rapidly progressive periodontitis

The plasma cell population in gingival biopsies from 3 groups of patients with adult, juvenile, and rapidly progressive periodontitis was characterized with respect to the distribution of individual immunoglobulin isotypes, including IgA subclasses, by paired immunofluorescence staining. The median ratios of IgG:IgA plasma cells in gingival connective tissue from the 3 groups were 2.7 (range 2.0-6.5), 3.0 (1.4-6.2), and 2.0 (1.2-4.0), respectively. Cells staining for intracellular IgM were found in low numbers in all biopsies (range 0.3-6.3% of all plasma cells). No statistically significant differences were observed between the 3 patient groups. In all 3 groups, the IgA plasma cell population was predominantly of the IgA1 isotype. One function of IgA seems to be to dampen inflammatory side-effects of other immune effector systems. The demonstrated predominance of IgA1 plasma cells indicates that the majority of IgA produced locally in gingivae of patients with periodontal diseases is susceptible to the IgA1-specific proteases excreted by important members of the disease-associated subgingival microflora. This may be an important factor in the apparently uncontrolled inflammation and tissue degradation taking place in the marginal periodontium during active periodontal disease.

Induction of human B cell differentiation by Fc region activators. I. Identification of an active tetrapeptide

Addition of pFc' fragments, composed of residues 334 to 446 in the Fc region of human IgG1, to cultures of human peripheral blood mononuclear cells resulted in the induction of Ig-secreting cells (ISC). Intact IgG1 and F(ab')2 fragments were inactive. The synthetic peptide p23, representing residues 335 to 357, retained the ISC-inducing property of pFc' fragments. The ISC response to p23 exhibited the isotype pattern IgMSC greater than IgGSC greater than or equal to IgASC. Results from cell depletion experiments revealed that the B cell response to p23 was T cell dependent but relatively monocyte independent. Cell proliferation was not increased in p23-stimulated PBMC cultures. Overlapping synthetic peptides based on the sequence of p23 were used to localize the active site in this molecule. These studies revealed that LPPSR (residues 351 to 355) was the sequence responsible for the ISC-inducing property of p23; however, expression of activity by this pentapeptide sequence could be dampened by N-flanking sequences. Finally, residue-deleted analogs of LPPSR were used to determine that LPPS was the minimum sequence retaining activity. Collectively, these data suggest that the fragmentation of IgG results in the expression of a tetrapeptide sequence with lymphocyte-stimulating properties.