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IgG Suppresses Antibody Responses in Mice Lacking C1q, C3, Complement Receptors 1 and 2, or IgG Fc-Receptors.

Bergström JJ, Heyman B - PLoS ONE (2015)

Bottom Line: This is used clinically in Rhesus prophylaxis, where administration of IgG anti-RhD prevents RhD-negative women from becoming immunized against RhD-positive fetal erythrocytes aquired transplacentally.The mechanisms by which IgG suppresses antibody responses are poorly understood.In conclusion, Fc-receptor binding or complement-activation by IgG does not seem to be required for its ability to suppress antibody responses to xenogeneic erythrocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.

ABSTRACT
Antigen-specific IgG antibodies, passively administered to mice or humans together with large particulate antigens like erythrocytes, can completely suppress the antibody response against the antigen. This is used clinically in Rhesus prophylaxis, where administration of IgG anti-RhD prevents RhD-negative women from becoming immunized against RhD-positive fetal erythrocytes aquired transplacentally. The mechanisms by which IgG suppresses antibody responses are poorly understood. We have here addressed whether complement or Fc-receptors for IgG (FcγRs) are required for IgG-mediated suppression. IgG, specific for sheep red blood cells (SRBC), was administered to mice together with SRBC and the antibody responses analyzed. IgG was able to suppress early IgM- as well as longterm IgG-responses in wildtype mice equally well as in mice lacking FcγRIIB (FcγRIIB knockout mice) or FcγRI, III, and IV (FcRγ knockout mice). Moreover, IgG was able to suppress early IgM responses equally well in mice lacking C1q (C1qA knockout mice), C3 (C3 knockout mice), or complement receptors 1 and 2 (Cr2 knockout mice) as in wildtype mice. Owing to the previously described severely impaired IgG responses in the complement deficient mice, it was difficult to assess whether passively administered IgG further decreased their IgG response. In conclusion, Fc-receptor binding or complement-activation by IgG does not seem to be required for its ability to suppress antibody responses to xenogeneic erythrocytes.

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IgG-mediated suppression of primary IgM-responses in C1q KO and C3 KO mice.C1q KO, C3 KO, and C57BL/6 mice were immunized with 50 μg IgGa anti-SRBC and 5x107 SRBC, 5x107 SRBC alone, or with 50 μg IgGa alone. (A,B) Five days after immunization, the number of spleen cells producing IgM anti-SRBC was assayed. Responses are shown as percentage of the direct PFC response/spleen in mice given SRBC alone (100%, open bars); black bars show responses in mice given IgG and SRBC. Direct PFC/spleen in the respective control groups (receiving antigen alone) were in A: C57BL/6, 56,105; C1q KO, 5,433 and in B: C57BL/6, 54,954; C3 KO, 3,614. Data are pooled from three experiments; (n = 4/group in each experiment). p-values denote comparisons between mice immunized with IgG anti-SRBC together with SRBC and mice immunized with SRBC alone. ***, p < 0.001.
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pone.0143841.g001: IgG-mediated suppression of primary IgM-responses in C1q KO and C3 KO mice.C1q KO, C3 KO, and C57BL/6 mice were immunized with 50 μg IgGa anti-SRBC and 5x107 SRBC, 5x107 SRBC alone, or with 50 μg IgGa alone. (A,B) Five days after immunization, the number of spleen cells producing IgM anti-SRBC was assayed. Responses are shown as percentage of the direct PFC response/spleen in mice given SRBC alone (100%, open bars); black bars show responses in mice given IgG and SRBC. Direct PFC/spleen in the respective control groups (receiving antigen alone) were in A: C57BL/6, 56,105; C1q KO, 5,433 and in B: C57BL/6, 54,954; C3 KO, 3,614. Data are pooled from three experiments; (n = 4/group in each experiment). p-values denote comparisons between mice immunized with IgG anti-SRBC together with SRBC and mice immunized with SRBC alone. ***, p < 0.001.

Mentions: To study the role of complement in IgG-mediated suppression, C57BL/6 mice, C1q KO and C3 KO mice were immunized with IgGa anti-SRBC and SRBC, SRBC alone or IgGa alone. The passively administered IgG anti-SRBC was prepared from mice with a different IgG allotype than the recipient mice, thus facilitating analysis only of the actively produced IgG. Spleens were harvested at day 5 after immunization and single cells producing SRBC-specific IgM were assayed in a direct hemolytic plaque forming cell (PFC) assay. IgG suppressed over 98% of the IgM-responses in C57BL/6, C1q KO, and C3 KO mice (Fig 1A and 1B). As expected, IgG efficiently suppressed the IgG anti-SRBC response in wildtype C57BL/6 mice (Figure A and D in S1 Fig). C1q KO and C3 KO mice generally have very poor antibody responses [22–24] and the IgG-response to SRBC administered alone in C1q KO or C3 KO mice was extremely low when the same serum dilution and incubation times as for C57BL/6 mice were used in the ELISA (Figure B and E in S1 Fig). Testing less diluted samples and extending the substrate incubation time to 3 h in the ELISA, a detectable IgG-response appeared also in C1q KO and C3 KO mice, albeit with high background levels (Figure C and F in S1 Fig). This response was significantly suppressed day 7 and 21 in C1q KO mice (Figure C in S1 Fig). IgG appeared to suppress also in C3 mice, although the differences were not significant (Figure F in S1 Fig).


IgG Suppresses Antibody Responses in Mice Lacking C1q, C3, Complement Receptors 1 and 2, or IgG Fc-Receptors.

Bergström JJ, Heyman B - PLoS ONE (2015)

IgG-mediated suppression of primary IgM-responses in C1q KO and C3 KO mice.C1q KO, C3 KO, and C57BL/6 mice were immunized with 50 μg IgGa anti-SRBC and 5x107 SRBC, 5x107 SRBC alone, or with 50 μg IgGa alone. (A,B) Five days after immunization, the number of spleen cells producing IgM anti-SRBC was assayed. Responses are shown as percentage of the direct PFC response/spleen in mice given SRBC alone (100%, open bars); black bars show responses in mice given IgG and SRBC. Direct PFC/spleen in the respective control groups (receiving antigen alone) were in A: C57BL/6, 56,105; C1q KO, 5,433 and in B: C57BL/6, 54,954; C3 KO, 3,614. Data are pooled from three experiments; (n = 4/group in each experiment). p-values denote comparisons between mice immunized with IgG anti-SRBC together with SRBC and mice immunized with SRBC alone. ***, p < 0.001.
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pone.0143841.g001: IgG-mediated suppression of primary IgM-responses in C1q KO and C3 KO mice.C1q KO, C3 KO, and C57BL/6 mice were immunized with 50 μg IgGa anti-SRBC and 5x107 SRBC, 5x107 SRBC alone, or with 50 μg IgGa alone. (A,B) Five days after immunization, the number of spleen cells producing IgM anti-SRBC was assayed. Responses are shown as percentage of the direct PFC response/spleen in mice given SRBC alone (100%, open bars); black bars show responses in mice given IgG and SRBC. Direct PFC/spleen in the respective control groups (receiving antigen alone) were in A: C57BL/6, 56,105; C1q KO, 5,433 and in B: C57BL/6, 54,954; C3 KO, 3,614. Data are pooled from three experiments; (n = 4/group in each experiment). p-values denote comparisons between mice immunized with IgG anti-SRBC together with SRBC and mice immunized with SRBC alone. ***, p < 0.001.
Mentions: To study the role of complement in IgG-mediated suppression, C57BL/6 mice, C1q KO and C3 KO mice were immunized with IgGa anti-SRBC and SRBC, SRBC alone or IgGa alone. The passively administered IgG anti-SRBC was prepared from mice with a different IgG allotype than the recipient mice, thus facilitating analysis only of the actively produced IgG. Spleens were harvested at day 5 after immunization and single cells producing SRBC-specific IgM were assayed in a direct hemolytic plaque forming cell (PFC) assay. IgG suppressed over 98% of the IgM-responses in C57BL/6, C1q KO, and C3 KO mice (Fig 1A and 1B). As expected, IgG efficiently suppressed the IgG anti-SRBC response in wildtype C57BL/6 mice (Figure A and D in S1 Fig). C1q KO and C3 KO mice generally have very poor antibody responses [22–24] and the IgG-response to SRBC administered alone in C1q KO or C3 KO mice was extremely low when the same serum dilution and incubation times as for C57BL/6 mice were used in the ELISA (Figure B and E in S1 Fig). Testing less diluted samples and extending the substrate incubation time to 3 h in the ELISA, a detectable IgG-response appeared also in C1q KO and C3 KO mice, albeit with high background levels (Figure C and F in S1 Fig). This response was significantly suppressed day 7 and 21 in C1q KO mice (Figure C in S1 Fig). IgG appeared to suppress also in C3 mice, although the differences were not significant (Figure F in S1 Fig).

Bottom Line: This is used clinically in Rhesus prophylaxis, where administration of IgG anti-RhD prevents RhD-negative women from becoming immunized against RhD-positive fetal erythrocytes aquired transplacentally.The mechanisms by which IgG suppresses antibody responses are poorly understood.In conclusion, Fc-receptor binding or complement-activation by IgG does not seem to be required for its ability to suppress antibody responses to xenogeneic erythrocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.

ABSTRACT
Antigen-specific IgG antibodies, passively administered to mice or humans together with large particulate antigens like erythrocytes, can completely suppress the antibody response against the antigen. This is used clinically in Rhesus prophylaxis, where administration of IgG anti-RhD prevents RhD-negative women from becoming immunized against RhD-positive fetal erythrocytes aquired transplacentally. The mechanisms by which IgG suppresses antibody responses are poorly understood. We have here addressed whether complement or Fc-receptors for IgG (FcγRs) are required for IgG-mediated suppression. IgG, specific for sheep red blood cells (SRBC), was administered to mice together with SRBC and the antibody responses analyzed. IgG was able to suppress early IgM- as well as longterm IgG-responses in wildtype mice equally well as in mice lacking FcγRIIB (FcγRIIB knockout mice) or FcγRI, III, and IV (FcRγ knockout mice). Moreover, IgG was able to suppress early IgM responses equally well in mice lacking C1q (C1qA knockout mice), C3 (C3 knockout mice), or complement receptors 1 and 2 (Cr2 knockout mice) as in wildtype mice. Owing to the previously described severely impaired IgG responses in the complement deficient mice, it was difficult to assess whether passively administered IgG further decreased their IgG response. In conclusion, Fc-receptor binding or complement-activation by IgG does not seem to be required for its ability to suppress antibody responses to xenogeneic erythrocytes.

Show MeSH
Related in: MedlinePlus