Lack of immunoglobulins does not prevent C1q binding to RGC and does not alter the progression of experimental glaucoma.
OBJECTIVE
The degeneration of retinal ganglion cells (RGC) in the glaucomatous retina is accompanied by activation of the classical complement cascade. The purpose of this study was to evaluate whether complement component C1q binding and activation of the complement cascade in the glaucomatous retina requires the presence of immunoglobulins.


METHODS
Experimental glaucoma was induced in normal mice and those carrying a targeted deletion of the RAG1 gene. Binding of C1q to RGC and accumulation of C3 and C5b-9 was investigated using immunohistochemical and proteomic approaches. Damage to the optic nerve and RGC was determined and compared between the two strains. Complement activation and accumulation were also evaluated in vitro using dissociated retinal cell cultures.


RESULTS
C1q was detected in the RGC layer in both RAG1(-/-) and control mice with elevated IOP, but not in mice with normal IOP. Proteomic analysis of retinal membrane fractions indicated that C1q and C3 are membrane bound to a similar degree in RAG1(-/-) and control mice with elevated IOP. The absence of Ig does not affect the rate of axonal damage or RGC loss. Furthermore, cultured RGC maintained in serum-free media are also C1q and C3 immunoreactive, demonstrating that Ig is not required for C1q binding to damaged RGC.


CONCLUSIONS
Our data demonstrate that lack of immunoglobulins and mature T/B cells does not influence the progression of glaucoma. Furthermore, immunoglobulins do not appear to be required for C1q binding and complement cascade activation on damaged RGC. These findings suggest that C1q recognizes an alternative binding partner expressed by stressed RGC.
Department of Ophthalmology and Visual Sciences, The University of Iowa, Iowa City, Iowa 52242, USA.
Qiong J
QJ
Ding
Amy C
AC
Cook
Alina V
AV
Dumitrescu
Markus H
MH
Kuehn
D000818:Animals; D002478:Cells, Cultured; D015922:Complement C1q / Q000276:immunology / Q000378:metabolism*; D003176:Complement C3 / Q000276:immunology / Q000378:metabolism; D004195:Disease Models, Animal; D018450:Disease Progression; D005901:Glaucoma / Q000276:immunology* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics; D007136:Immunoglobulins / Q000276:immunology / Q000378:metabolism*; D007150:Immunohistochemistry; D007153:Immunologic Deficiency Syndromes / Q000276:immunology* / Q000378:metabolism; D007429:Intraocular Pressure / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009900:Optic Nerve / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D040901:Proteomics; D012165:Retinal Ganglion Cells / Q000276:immunology* / Q000378:metabolism / Q000473:pathology
D003176:Complement C3; D018398:Homeodomain Proteins; D007136:Immunoglobulins; C064658:RAG-1 protein; D015922:Complement C1q