An inherited deficiency of the third component of complement, C3, in guinea pigs

Effect of Parental Age, Parity, and Pairing Approach on Reproduction in Strain 13/N Guinea Pigs (Cavia porcellus)

Guinea pigs are important animal models for human disease, and both outbred and inbred lines are utilized in biomedical research. The optimal maintenance of guinea pig colonies, commercially and in research settings, relies on robust informed breeding programs, however, breeding data on specialized inbred strains are limited. Here, we investigated the effects of parental age, parity, and pairing approaches on mean total fetus count, percentage of female pups in the litter, and pup survival rate after 10 days in strain 13/N guinea pigs. Our analysis of colony breeding data indicates that the average litter size is 3.3 pups, with a 25.2% stillbirth rate, a failure-to-thrive outcome in 5.1% of pups, and a 10 day survival rate of 69.7%. The only variable to significantly affect the reproductive outcomes examined was parental age (p < 0.05). In comparison to adults, both juvenile and geriatric sows had lower total fetus counts; juvenile boars had a higher percentage of females in litters, and geriatric boars had a lower 10 day survival rate of pups. These studies provide valuable information regarding the reproductive characteristics of strain 13/N guinea pigs, and support a variety of breeding approaches without significant effects on breeding success.

Generation of complement protein C3 deficient pigs by CRISPR/Cas9-mediated gene targeting

Complement protein C3 is the pivotal component of the complement system. Previous studies have demonstrated that C3 has implications in various human diseases and exerts profound functions under certain conditions. However, the delineation of pathological and physiological roles of C3 has been hampered by the insufficiency of suitable animal models. In the present study, we applied the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) system to target the C3 gene in porcine fetal fibroblasts. Our results indicated that CRISPR/Cas9 targeting efficiency was as high as 84.7%, and the biallelic mutation efficiency reached at 45.7%. The biallelic modified colonies were used as donor for somatic cell nuclear transfer (SCNT) technology to generate C3 targeted piglets. A total of 19 C3 knockout (KO) piglets were produced and their plasma C3 protein was undetectable by western blot analysis and ELISA. The hemolytic complement activity and complement-dependent cytotoxicity assay further confirmed that C3 was disrupted in these piglets. These C3 KO pigs could be utilized as a valuable large animal model for the elucidation of the roles of C3.

Detection of two variants of complement component C3 in C3-deficient guinea pigs distinguished by the absence and presence of a thiolester

The complement system is an essential part of the innate defense, and C3 is an integral part of this powerful system. In previously identified complement C3 deficient guinea pigs only approx. 5% of the normal serum C3 level is detectable. No differences were found between in vitro C3 protein synthesis and C3 mRNA levels of cells from C3-deficient and wild-type animals and the amino acid sequences of both C3 proteins are identical as deduced from cDNA sequencing. Previously, the principal inability to form a C3 thiolester was discussed as a possible reason for this C3-deficiency. Here we report the isolation of two functionally different C3 species from the C3-deficient animals. Only one of these C3 proteins exhibits normal hemolytic activity and contains a thiolester group. The second C3 species is exclusively present in C3-deficient animals and lacks a thiolester, explaining its failure to express hemolytic activity. The presence of a second C3 species lacking a thiolester structure only in C3-deficient animals indicates that the stability of the thiolester may play a role in C3 deficiency. However further analysis of the in vitro stability of the thiolesters of C3 from normal and C3-deficient guinea pigs revealed no differences. A decreased in vivo thiolester stability might lead to the presence of C3 with and without a thiolester or alternatively the expression of two isoforms of C3 in these animals. Considering the central role of C3 in host defense, the mechanisms of C3 thiolester formation require further analysis.

Herpes simplex virus type 1 glycoprotein gC mediates immune evasion in vivo

Many microorganisms encode proteins that interact with molecules involved in host immunity; however, few of these molecules have been proven to promote immune evasion in vivo. Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC) binds complement component C3 and inhibits complement-mediated virus neutralization and lysis of infected cells in vitro. To investigate the importance of the interaction between gC and C3 in vivo, we studied the virulence of a gC-null strain in complement-intact and C3-deficient animals. Using a vaginal infection model in complement-intact guinea pigs, we showed that gC-null virus grows to lower titers and produces less severe vaginitis than wild-type or gC rescued virus, indicating a role for gC in virulence. To determine the importance of complement, studies were performed with C3-deficient guinea pigs; the results demonstrated significant increases in vaginal titers of gC-null virus, while wild-type and gC rescued viruses showed nonsignificant changes in titers. Similar findings were observed for mice where gC null virus produced significantly less disease than gC rescued virus at the skin inoculation site. Proof that C3 is important was provided by studies of C3 knockout mice, where disease scores of gC-null virus were significantly higher than in complement-intact mice. The results indicate that gC-null virus is approximately 100-fold (2 log10) less virulent that wild-type virus in animals and that gC-C3 interactions are involved in pathogenesis.

Molecular Analysis of the Third Component of Canine Complement (C3) and Identification of the Mutation Responsible for Hereditary Canine C3 Deficiency

Genetically determined deficiency of the third component of complement (C3) in the dog is characterized by a predisposition to recurrent bacterial infections and to type 1 membranoproliferative glomerulonephritis. The current studies were undertaken to characterize the cDNA for wild-type canine C3 and identify the molecular basis for hereditary canine C3 deficiency. Amplification, cloning, and sequence analysis indicated that canine C3 is highly conserved in comparison with human, mouse, and guinea pig C3. Southern blot analysis failed to show any gross deletions or rearrangements of DNA from C3-deficient animals. Northern blot analysis indicated that the livers of these animals contain markedly reduced quantities of a normal length C3 mRNA. The full-length 5.1-kb canine C3 cDNA was amplified in overlapping PCR fragments. Sequence analysis of these fragments has shown a deletion of a cytosine at position 2136 (codon 712), leading to a frameshift that generates a stop codon 11 amino acids downstream. The deletion has been confirmed in genomic DNA, and its inheritance has been demonstrated by allele-specific oligonucleotide hybridization.

Follicular dendritic cells and presentation of antigen and costimulatory signals to B cells

This review focuses on how immunogens trapped by FDC in the form of Ag-Ab complexes productively signal B cells. In vitro. Ag-Ab complexes are poorly immunogenic but in vivo immune complexes elicit potent recall responses. FDC trap Ag-Ab complexes and make immune complex coated bodies or "iccosomes". B cells endocytose iccosomes, the Ag is processed, and T-cell help is elicited. In vitro, addition of FDC bearing appropriate Ag-Ab complex to memory T and B cells provoke potent recall responses (IgG and IgE). FDC also provide nonspecific costimulatory signals which augment B-cell proliferation and Ab production. B cell-FDC contact is important and interference with ICAM-1-LFA-1 interactions reduces FDC-mediated costimulation. Preliminary data suggest that a costimulatory signal may be delivered via CR2L on FDC binding CR2 on B cells. FDC can also stimulate B cells to become chemotactically active and can protect lymphocytes from apoptosis. FDC also appear to be rich in thiol groups and may replace reducing compounds such as 2 mercaptoethanol in cultures. In short, FDC-Ag specifically signals B cells through BCR, and FDC provide B cells with iccosomal-Ag necessary for processing to elicit T-cell help. In addition, FDC provide nonspecific signals that are important to promote B-cell proliferation, maintain viability, and induce chemotactic responsiveness.

Hereditary deficiency of C3 in animals and humans

Inherited deficiency of complement C3 has been described in guinea pigs, dogs and 20 humans. Homozygous deficiency of C3 is associated with recurrent pyogenic infections by encapsulated bacteria, especially H. influenzae, S. pneumoniae and N. meningitidis. In dogs and humans there is also an association with development of glomerulonephritis of the mesangiocapillary type. Some patients also develop transient erythematous rashes in association with pyogenic infections, with histology showing predominantly neutrophil infiltration and small vessel vasculitis. Studies of antibody responses, mainly in experimental animals have shown impaired primary and secondary responses to both thymus-dependent and -independent antigens at low immunizing doses, with a reduced switch from IgM to IgG production. The molecular basis of C3 deficiency has been established in two humans with C3 deficiency. In one it was due to a splice junction mutation and in another, to a partial gene deletion. These mutations are not compatible with the production of functional C3 in any tissue. Such patients with absolute C3 deficiency are a valid model for understanding the physiological role of C3 in vivo.

Macrophage-bound C3 fragments as adhesion molecules modulate presentation of exogenous antigens

The involvement of complement in the response to T cell dependent antigens is generally accepted, however the mechanism has not been clarified. We compared the T cell response in vitro, using antigen-pulsed macrophages from normal and genetically C3-deficient guinea pigs, and show, that C3-fragments fixed covalently to the surface of the antigen-presenting cells are involved in the triggering of responder T cells. Binding of guinea pig C3-specific mAb to oil-elicited, OVA- and PPD-pulsed macrophages of C3D guinea pigs is reduced compared to normal cells, while the expression of Ia antigens is the same. C3-like peptides can be immunoprecipitated only from the lysate of oil-elicited normal cells. These C3-fragments are fixed to the cell-membrane via ester-bonds, since they are released upon treatment with hydroxylamine. In comparison with normal cells, the antigen-presenting capacity of macrophages derived from C3D animals is strongly impaired in cultures containing 10% normal guinea pig serum. A further impairment is observed in cultures with 10% C3D guinea pig serum. Two of the tested C3-specific mAb inhibited antigen-induced T cell proliferation in a dose-dependent manner. Our data point to the importance of C3, as a bivalent molecule, having the capacity to facilitate the cooperation between the antigen-presenting cell and the responder T lymphocytes.

The role of C3 in the immune response

The complement system, particularly the third component, plays an important modulatory role in the inductive phase of the immune response. As discussed here by Anna Erdei and colleagues, the picture that is emerging is that immobilized C3 split products facilitate the cooperation between immunocompetent cells and are co-stimulatory molecules in T- and B-cell activation, probably as a result of their ability to promote cell-cell adhesion. In contrast, soluble C3 products inhibit lymphocyte proliferation.

Molecular basis of complement C3 deficiency in guinea pigs

In experiments to ascertain the biochemical basis of a genetically determined deficiency of the third component of complement (C3) in guinea pigs, we found that C3-deficient liver and peritoneal macrophages contain C3 messenger RNA of normal size (approximately 5 kb) and amounts, that this mRNA programs synthesis of pro-C3 in oocytes primed with liver RNA and in primary macrophage cultures. In each instance, heterodimeric native C3 protein was secreted with normal kinetics but the C3 protein product of the deficient cells failed to undergo autolytic cleavage and was unusually susceptible to proteolysis. These data and a selective failure of C3 in plasma of deficient animals to incorporate [14C]methylamine suggested either a mutation in primary structure of the C3 protein or a selective defect in co- or postsynthetic processing affecting the thiolester bridge, a structure important for C3 function. A mutation in the primary structure of C3 was ruled out by comparison of direct sequence analysis of C3 cDNA generated from two C3 deficient and two C3 sufficient guinea pig liver libraries. Three base pair differences, none resulting in derived amino acid sequence differences were identified. Finally, restriction fragment length polymorphisms were identified in the C3 gene that are independent of the deficiency phenotype. This marker of the C3 gene permits testing of these hypotheses using molecular biological and classical genetic methods.

Phototoxic erythema following PUVA treatment: independence of complement

The effect of PUVA treatment on normal human serum (NHS), on isolated PMN, or on C3-deficient guinea pigs and congenic (C3-competent) control animals was tested. At a concentration of 0.1 or 1 mM/l 8-MOP and UVA doses of 5-30 J/cm2, PUVA failed to induce any detectable C3-cleavage in NHS. Furthermore, when the complement (C) activation in NHS had been induced before or after PUVA treatment by various methods. PUVA did not modulate the extent of C3-cleavage. PUVA did not affect the viability of isolated PMN, nor did it induce a release of LDH or elastase. No differences between C3-deficient and C-competent guinea pig skin exposed to PUVA were observed in erythema or histologic responses. Immunohistologic examination of specimens from normal guinea pigs revealed C3b and C3d deposits on necrotic keratinocytes, findings restricted to the PUVA-treated areas. Necrosis of keratinocytes was present in skin specimens of C3-deficient animals from PUVA-treated sites to a similar extent. However, deposits of C3-related antigens were completely absent there. From these observations, we suggest that the induction of phototoxic erythema following PUVA treatment is independent of complement.

Impaired humoral immune response in complement C3-deficient guinea pigs: absence of secondary antibody response

A recently described genetically controlled C3 deficiency (C3D) in guinea pigs (GP) provided a unique model for studying the role of C3 in the afferent limb of the humoral immune response in a direct manner. These C3D animals, which have only 5-7% of normal serum C3 level, were immunized with the bacteriophage phi chi 174, a T cell-dependent antigen, followed by a booster injection after 4 weeks (1.5 X 10(9) plaque-forming units/kg). The formation of IgM and IgG antibody in the course of the primary and secondary response was determined and compared with a control group of inbred strain 2 GP. The C3D animals showed a markedly diminished antibody response to this antigen. Amplification of the antibody titer as well as regular isotype switching from IgM to IgG was absent in the secondary response. Increasing the amount of antigen to a high dose (1 X 10(10) plaque-forming units/kg) led to a normalization of the antibody response. The impairment in antibody formation resembles closely the impaired antibody response in C4-deficient or C2-deficient GP, which both have a block in activation of C3 via the classical pathway. However, in contrast to C4D GP or C2D GP the C3D GP do not exhibit serological characteristics of immune complex disease. They have normal levels of total serum IgM, of IgM anti-2,4-dinitrophenyl antibodies and of IgM rheumatoid factors.