Effect of intravenous immunoglobulin administration on erythrocyte and leucocyte parameters.

BACKGROUND: Intravenous immunoglobulins (IVIG) are an attractive therapeutic tool for therapy of toxic epidermal necrolysis and severe forms of certain autoimmune diseases, including dermatomyositis, autoimmune blistering diseases, systemic vasculitis and lupus erythematodes. OBJECTIVES: Prompted by a case of IVIG-associated haemolytic anaemia, the effects of IVIG administrations on haematological parameters in patients with dermatological conditions were investigated. METHODS: Erythrocyte and leucocyte parameters were retrospectively analysed in 16 patients who had received IVIG at doses from 1 to 3 g/kg bodyweight (n = 35 cycles). The influence of IVIG on leucocyte survival was determined in vitro. RESULTS: Decreased absolute erythrocyte numbers, haemoglobin and haematocrit levels and a case of haemolytic anaemia were linked to transfusion of high-, but not low-dose IVIG. In contrast, leucopenia post-IVIG occurred in the vast majority of the recipients, unrelated to the administered IVIG amounts. In vitro investigations revealed a dose-dependent impairment of cell survival by IVIG in the neutrophil and monocyte, but not in the lymphocyte subpopulations. In several IVIG preparations, substantial amounts of blood group anti-A/anti-B antibodies were detected which could have accounted for the observed changes in the haematological parameters in our study cohort. CONCLUSIONS: IVIG products should be administered strictly according to indications. Commercially available IVIG products can contain blood group-specific antibodies that may induce haemolysis in some recipients. Monitoring of blood counts during applied IVIG therapy, especially when high doses are administered, is recommended.

Difference in release kinetics of unwashed and washed platelet-released supernatants from bone substitute materials: the impact of platelet preparation modalities.

BACKGROUND AND OBJECTIVE: In regenerative dentistry, platelet preparations are applied to stimulate bone healing and periodontal regeneration. Here, we pursue a strategy where bone substitutes are used as carriers for platelet-released supernatants. The mitogenic capacity and release kinetics of loaded bone substitutes were assessed. MATERIAL AND METHODS: Platelet-released supernatants of washed platelets (washed PRS) and platelet-released supernatants of unwashed platelets (unwashed PRS) were lyophilized onto the bone substitutes deproteinized bovine bone mineral, hydroxyapatite and ß-tricalcium phosphate. Scanning electron microscopy images were taken. Supernatants of bone substitutes were collected at hours 1, 3, 6, 24, and 48 and medium was replaced. We evaluated the protein content with the bicinchoninic acid assay and the effect on proliferation using bioassays with human periodontal fibroblasts. Release of growth factors from the loaded bone substitutes was measured based on the platelet-derived growth factor isoform (PDGF-BB) and thrombin immunoassays. Furthermore, we assessed DNA and RNA content of washed PRS and unwashed PRS. RESULTS: Unwashed PRS showed higher total protein concentrations than washed PRS, while the concentration of PDGF-BB, thrombin, DNA, RNA and their mitogenic effect was not significantly different. The bone substitute materials adsorbed protein over time but no significant changes in overall appearance was found. Supernatants collected from unwashed PRS-loaded bone substitute after 1 h induced a potent mitogenic response in periodontal fibroblasts. This pro-mitogenic capacity of the supernatants decreased over the observation period. Supernatants of washed PRS-loaded bone substitutes did not induce a substantial mitogenic effect. Levels of PDGF-BB, thrombin and protein were higher in supernatants of unwashed PRS-loaded bone substitutes than of washed PRS-loaded bone substitutes. CONCLUSION: Bone substitutes loaded with unwashed PRS, but not bone substitutes loaded with washed PRS show continuously declining release kinetics. These data suggest that plasma components in platelet preparations can modify the release kinetics profile.

Red blood units collected from bone marrow harvests after mononuclear cell selection qualify for autologous use.

BACKGROUND: After large volume bone marrow (BM) harvest, donors and patients can develop severe anaemia, because collected BM can contain up to 20% of their red cell mass. In a prospective analysis, we investigated the feasibility to recover red blood cells (RBCs) from the harvested BM and investigated whether these RBC units meet the quality requirements of the European Council. PATIENTS AND METHODS: From 19 patients (median age 51 yrs, range 31-77) with acute myocardial infarction, who participated in the MYSTAR study, a median volume of 1299 ml (range, 700-1870 ml) BM was collected. During BM processing, mononuclear cells (MNC) were separated using the Cobe Spectra apheresis system and the residual RBCs were collected in a separate bag. The quality of the collected RBCs was assessed by measuring LDH, free haemoglobin, potassium and lactate. Haemolysis was calculated and the intracellular concentration of ATP, ADP, AMP was determined by HPLC. RESULTS: RBC units recovered from BM after MNC separation had a mean volume of 312 +/- 95 ml with a haematocrit of 47 +/- 8.9%, a haemoglobin content of 51 +/- 15 g per unit, a haemolysis of 0.15 +/- 0.005%, a pH of 6.8 +/- 0.007 and an intracellular ATP concentration of 135 pmol/10(6) RBC +/- 41, which is comparable with freshly collected packed red blood cells (PRBCs). CONCLUSION: RBCs, collected from bone marrow harvests, can be used for autologous blood support to minimize allogeneic blood transfusions in donors and patients after large volume BM donation.

Dependence of germinal center B cells on expression of CD21/CD35 for survival.

Affinity-driven selection of B lymphocytes within germinal centers is critical for the development of high-affinity memory cells and host protection. To investigate the role of the CD21/CD35 coreceptor in B cell competition for follicular retention and survival within the germinal center, either Cr2+ or Cr2null lysozyme-specific transgenic B cells were adoptively transferred into normal mice immunized with duck (DEL) or turkey (TEL) lysozyme, which bind with different affinities. In mice injected with high-affinity turkey lysozyme, Cr2null B cells responded by follicular retention; however, they could not survive within germinal centers. This suggests that CD21 provides a signal independent of antigen that is required for survival of B cells in the germinal center.

Shift of C3 deposition from localization in the glomerulus into the tubulo-interstitial compartment in the absence of secreted IgM in immune complex glomerulonephritis.

The role of secretory IgM in protecting kidney tissue from immune complex glomerulonephritis induced by 4 mg horse spleen apoferritin and 0.05 mg lipopolysaccharide has been investigated in mutant mice in which B cells do not secrete IgM, but are capable of expressing surface IgM and IgD and secreting other Ig isotypes. Glomerular size, number of glomeruli per cross-section, glomerular cellularity and urine content of protein and creatinine was comparable in treated secreted IgM (sIgM)-deficient and wild-type mice. Assessment of urinary proteins by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed a 30 kDa low molecular weight protein in treated sIgM-deficient animals only, reflecting dysfunction of proximal tubules. A shift of bound C3 from glomeruli to the tubulo-interstitial compartment in sIgM-deficient mice also suggests tubulo-interstitial damage. In contrast, local C3 synthesis within the kidney tissue did not differ between the two treated groups. Apoptosis physiologically present to maintain kidney cell homeostasis was increased slightly in treated wild-type mice. These results indicate that secretory IgM can protect the tubulo-interstitial compartment from immune complex-induced damage without having an effect on the glomerulus.

Statin treatment reduces matrix degradation capacity of proinflammatory polarized macrophages.

BACKGROUND AND AIMS: Macrophages are versatile immune cells involved in tissue degradation and remodeling. Proinflammatory macrophages have the highest capacity of matrix degradation and proteolysis. Within atherosclerotic lesions, proinflammatory macrophages are associated with unstable plaques. Statins have been demonstrated to increase plaque stability. Possible changes of polarized macrophage tissue degradation behavior under statin treatment are currently unknown. METHODS: Polarized macrophages were tested in vitro for matrix degradation capacity with or without statin treatment. RESULTS: Proinflammatory macrophages show high matrix degradation capacity, which is lost after statin treatment. Statin concentrations were within a physiological range and did not influence overall macrophage polarization. Proinflammatory macrophages showed however a loss of filopodia where activators of MMPs are located. Loss of matrix degradation in proinflammatory macrophages was associated with changes of MMP14 activation and loss of uPAR localization at filopodia. Supplementation of mevalonate restored localization of uPAR to cellular protrusions and matrix degradation capacity. CONCLUSION: Statins reduce the matrix degradation potential of proinflammatory macrophages by reducing uPAR localization to cellular filopodia and reducing intracellular MMP14 activation.

Complement and the immune response.

This past year has seen a major advance in our understanding of how the complement system enhances the adaptive immune response. The use of in vivo models has revealed that direct coupling of C3d to antigen is sufficient to dramatically reduce the amount of antigen required for a secondary response. At least one important requirement for the enhancing effect was determined to be expression of the CD21 (C3d receptor) on B cells.

Platelet-borne complement proteins and their role in platelet-bacteria interactions.

Essentials Platelets play an important role in pathogen recognition. Platelets contain several complement factors and can interact with E. coli. Platelet's complement protein C3 differs from plasmatic C3 in its electrophoretic mobility. Upon contact with bacteria, platelets are activated and can enhance complement activation. SUMMARY: Background The role of platelets in immune defense is increasingly being recognized. Platelets bind complement proteins from plasma, initiate complement activation, and interact with bacteria. However, the contribution of platelets to complement-mediated defense against bacterial infections is not known in detail. Objectives To assess platelet interactions with Escherichia coli strains, and evaluate the contributions of platelet complement proteins to host defense. Methods We studied the cell-cell interactions of a pathogenic and a non-pathogenic E. coli strain with platelet concentrates, washed platelets and manually isolated platelets by flow cytometry and ELISA. The presence of complement proteins and complement RNA in megakaryocytes and platelets was analyzed by PCR, RT-PCR, confocal microscopy, and western blotting. Results Incubation with E. coli leads to platelet activation, as indicated by the expression of CD62P and CD63 on the platelet surface. RNA and protein analyses show that megakaryocytes and platelets contain complement C3, and that platelet C3 migrates differently on polyacrylamide gels than plasmatic C3. Activation of platelets by bacteria leads to translocation of C3 to the cell surface. This translocation is not induced by thrombin receptor activating peptide or lipopolysaccharide. Interaction of platelets with E. coli occurs even in the absence of plasma proteins, and is independent of platelet toll-like receptor 4 and α2b ß3 (glycoprotein IIbIIIa). Conclusion Platelets contain a specific form of C3. Importantly, they can modulate immune defense against bacteria by enhancing plasmatic complement activation.

Defective TCR surface expression associated with impaired TCR beta-chain assembly in a patient with cutaneous T-cell lymphoma.

We report on a patient with cutaneous T-cell lymphoma (CTCL) of long-standing duration. Phenotypic analysis of his peripheral blood mononuclear cells revealed an increased CD4+ T-helper subset and a decreased CD8+ cytotoxic T-cell population. Eighty-three to ninety-three percent of the patient's CD4+ T cells in the peripheral blood and 70% of the CD4+ T cells in the lesional skin lacked surface expression of the TCR/CD3 complex and showed a clonal rearrangement pattern of the TCR gamma-chain gene (V11-J1/J2). The lack in TCR surface expression correlated with defective assembly of the TCR beta-chain. Although mRNA for the TCR constant region beta 1 was found in the patient's purified CD4+ TCR-CD3- T cells, no intracytoplasmic TCR beta protein was detectable. In contrast, the patient's purified CD4+ TCR-CD3- T cells not only expressed mRNA specific for the TCR alpha-chain and for all CD3 chains, but intracytoplasmic TCR alpha and CD3 epsilon proteins could also be found. The lack of TCR beta protein clearly explains the defective surface expression of the TCR/CD3 complex in the patient's malignant T cells.

Transgenic and knockout mice in research on prion diseases.

Since the discovery of the prion protein (PrP) gene more than a decade ago, transgenetic investigations on the PrP gene have shaped the field of prion biology in an unprecedented way. Many questions regarding the role of PrP in susceptibility of an organism exposed to prions have been elucidated. For example mice with a targeted disruption of the PrP gene have allowed the demonstration that an organism that lacks PrPc is resistant to infection by prions. Reconstitution of these mice with mutant PrP genes allowed investigations on the structure-activity relationship of the PrP gene with regard to scrapie susceptibility. Unexpectedly, transgenic mice expressing PrP with specific amino-proximal truncations spontaneously develop a neurologic syndrome presenting with ataxia and cerebellar lesions. A distinct spontaneous neurologic phenotype was observed in mice with internal deletions in PrP. Using ectopic expression of PrP in PrP knockout mice has turned out to be a valuable approach towards the identification of host cells that are capable of replicating prions. Transgenic mice have also contributed to our understanding of the molecular basis of the species barrier for prions. Finally, the availability of PrP knockout mice and transgenic mice overexpressing PrP allows selective reconstitution experiments aimed at expressing PrP in neurografts or in specific populations of hemato- and lymphopoietic cells. Such studies have shed new light onto the mechanisms of prion spread and disease pathogenesis.

Platelet-released supernatants stimulate formation of osteoclast-like cells through a prostaglandin/RANKL-dependent mechanism.

Platelets are activated at fracture sites or upon the insertion of implants as a consequence of vascular disruption and secrete the contents of their granules into the developing hematoma. The regeneration of injured tissue requires bone remodeling and the resorbing activity of osteoclasts. To test our hypothesis that platelets can stimulate osteoclastogenesis, we examined the effects of supernatants released from thrombin-activated platelets on osteoclast-like cell formation in murine bone marrow cultures. Histochemical analysis indicated the presence of bone-resorbing, tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. Transcripts that are characteristically expressed in native osteoclasts were increased in these cultures, as determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. The inhibition of both cyclooxygenases with indomethacin, as well as the addition of the cyclooxygenase-2 (COX-2)-selective antagonist, NS398, completely blocked osteoclast-like cell formation and decreased endogenous prostaglandin E(2) production. Platelet-released supernatants stimulated the expression of receptor activator of NF-kappaB ligand (RANKL), whereas mRNA levels of osteoprotegerin (OPG) were decreased. The formation of osteoclast-like cells was prevented by recombinant OPG. Our results suggest that COX-2 activity is necessary for osteoclast-like cell formation in response to platelet-released supernatants, and that endogenously produced prostaglandin E(2) can, in turn, increase the RANKL:OPG ratio, indicating that platelets can contribute to bone remodeling by stimulation of osteoclastogenesis.

Beta2-adrenergic receptor agonists reduce proliferation but not protein synthesis of periodontal fibroblasts stimulated with platelet-derived growth factor-BB.

OBJECTIVE: Catecholamines released from ß-adrenergic neurons upon stress can interfere with periodontal regeneration. The cellular mechanisms, however, are unclear. Here, we assessed the effect of catecholamines on proliferation of periodontal fibroblasts. METHODS: Fibroblasts from the gingiva and the periodontal ligament were exposed to agonists of the ß-adrenergic receptors; isoproterenol (ISO, non-selective ß-adrenergic agonist), salbutamol (SAL, selective ß2-adrenergic receptor agonist) and BRL 37344 (BRL selective ß3-receptor agonist). Proliferation was stimulated with platelet-derived growth factor-BB (PDGF-BB). Pharmacological inhibitors and gene expression analysis further revealed ß-adrenergic signalling. RESULTS: Gingiva and periodontal ligament fibroblast express the ß2-adrenergic receptor. ISO and SAL but not BRL decreased proliferation of fibroblasts in the presence of PDGF-BB. The inhibitory effect of ß-adrenergic signalling on proliferation but not protein synthesis in response to PDGF-BB was reduced by propranolol, a non-selective ß-adrenergic antagonist. CONCLUSIONS: These results suggest that ß2-receptor agonists can reduce the mitogenic response of periodontal fibroblasts. These data add to the compelling concept that blocking of ß2-receptor signalling can support tissue maintenance and regeneration.

Apheresis products of the Amicus and the AS.TEC 204 cell separators are comparable with regard to dendritic cells derived from the mononuclear cell collection.

BACKGROUND: In this study, we investigated the quality of autologous mononuclear cells (MNC) collected with two different cell separators using standard MNC-apheresis procedure modalities. MNCs were purified by density gradient centrifugation and cultured according to standard protocols to generate dendritic cells (DC) and 1 x 10(7)/ml immature DCs were pulsed with tumour lysate for 3 days and subsequently characterized by fluorescent-activated cell sorter analysis. RESULTS: No difference was found in the monocyte content of either apheresis product (P = 0.07) and in the overall yield of MNCs (P = 0.7). Mature DCs as defined by their phenotype revealed also no significant difference: Amicus, 118 x 10(6) cells +/- 91 vs. AS.TEC 204, 128 x 10(6) cells +/- 137 (P = 0.55), respectively, although the contamination with platelets (threefold) and red cells (twofold) was significantly higher in the AS.TEC 204 group (P < 0.05) than in the Amicus group. CONCLUSION: The Amicus and the AS.TEC 204 are equally capable in providing MNCs for the generation of DCs and the amount of concomitantly collected red cells and platelets had no impact on the final DC yield.

STRO-1+ mesenchymal precursor cells located in synovial surface projections of patients with osteoarthritis.

OBJECTIVE: To investigate the presence of mesenchymal precursor cells (MPCs) in synovial surface projections of patients with osteoarthritis (OA), to characterize their phenotype and to show their localization. METHODS: Progenitor cells in synovial surface projections were identified by immunohistochemistry, morphometric analysis and confocal laser scanning microscopy using the following phenotypic markers: STRO-1, CD34, and alpha smooth muscle actin (alpha-SMA). RESULTS: In the synovial tissue of all 21 patients with OA MPCs were detected. Immunohistochemistry and subsequent morphometric analysis showed that approximately twice as many STRO-1+ cells/mm2 were observed in synovial tissue of patients with OA as compared to healthy organ donors and that number of STRO-1+ cells/mm2 correlated with total cell number/mm2. Interestingly, in the synovial tissue of patients with OA, twice as many STRO-1+ cells/mm2 were found in synovial surface projections as compared to the sublining area without villi. Using confocal laser scanning microscopy two populations of STRO-1+ MPCs could be detected in synovial surface projections. Single STRO-1+ cells that co-expressed alpha-SMA resemble a population of pericyte precursors required to stabilize the immature vasculature. The second STRO-1+ cell population that was found lacked alpha-SMA but co-expressed CD34 on their surface with low intensity. CONCLUSION: Here we can show that in the synovial tissue of patients with OA twice as many STRO-1+ MPCs can be found in synovial surface projections as compared to the sublining area. These cells are preferentially located at the basis and in the protruding end of the synovial surface projection.

Binding of disease-associated prion protein to plasminogen.

Transmissible spongiform encephalopathies are associated with accumulation of PrP(Sc), a conformer of a cellular protein called PrP(C). PrP(Sc) is thought to replicate by imparting its conformation onto PrP(C) (ref. 1), yet conformational discrimination between PrP(C) and PrP(Sc) has remained elusive. Because deposition of PrP(Sc) alone is not enough to cause neuropathology, PrP(Sc) probably damages the brain by interacting with other cellular constituents. Here we find activities in human and mouse blood which bind PrP(Sc) and prion infectivity, but not PrP(C). We identify plasminogen, a pro-protease implicated in neuronal excitotoxicity, as a PrP(Sc)-binding protein. Binding is abolished if the conformation of PrP(Sc) is disrupted by 6M urea or guanidine. The isolated lysine binding site 1 of plasminogen (kringles I-III) retains this binding activity, and binding can be competed for with lysine. Therefore, plasminogen represents the first endogenous factor discriminating between normal and pathological prion protein. This unexpected property may be exploited for diagnostic purposes.

Concurrence of sarcoidosis and aortitis: case report and review of the literature.

Takayasu arteritis (TA) is a rare manifestation of systemic large vessel vasculitis which affects predominantly the aorta and its main branches, but often remains unrecognised owing to delayed diagnosis and non-characteristic clinical features. Sarcoidosis, too, is a systemic inflammatory disease which can affect virtually any organ system. Reports about the coincidence of both diseases have appeared. The case presented here is characterised by a significant time lag between detection of TA and appearance of clinical signs of sarcoidosis. The woman, now 39 years old, had erythema nodosum, circumscript alopecia, and recurrent uveitis, which dated back to 1980 and was attributed to sarcoidosis. At least 12 years later aortic valve insufficiency with progressive cardiac failure developed. Histology performed at the time of aortic valve prosthesis in 1997 disclosed a diagnosis of TA, which was confined to the aortic root. Incidentally, sarcoidosis was diagnosed in adjacent lymph nodes. A thorough check up failed to detect further manifestations of TA; thus, possibly, the patients had aortitis similar to, but not identical with, TA. Several related cases previously reported are discussed, suggesting that both diseases may be inherently related as they are characterised by certain non-specific, immunoinflammatory abnormalities. This case report suggests that the prevalence of TA, or related forms of arteritis, may be higher than expected and should be considered, especially in younger patients with non-characteristic cardiovascular symptoms and suspected systemic inflammatory disease. Moreover, the association with sarcoidosis in this and other previously described cases suggests that the two diseases may be related and that TA or TA-like vasculitis may even be a complication of sarcoidosis.

Increased expression of the blood group-related Lewis Y antigen on synovial fluid granulocytes of patients with arthritic joint diseases.

OBJECTIVE: To evaluate the expression of the carbohydrate structures Lewis Y (LeY), sialyl-LeX (sLeX) and Lewis X (LeX) on paired peripheral blood (PB) and synovial fluid (SF) granulocytes in patients with arthritic diseases. METHODS: Ten patients with rheumatoid arthritis (RA), seven patients with spondyloarthritis (SA) and eight patients with osteoarthritis (OA) were studied. Granulocyte expression of the Le oligosaccharides was analysed by fluorescence-activated cell sorting. RESULTS: SF granulocytes of patients with RA, SA and OA expressed higher levels of the LeY oligosaccharide than PB granulocytes. Increases in LeY on SF granulocytes were similar in all three underlying diseases. No differences in the expression of the Le antigens were detected between PB granulocytes of patients and healthy individuals. Expression of sLeX and LeX showed no variation between SF and PB neutrophils. CONCLUSION: The selective increase in LeY antigen on SF granulocytes in RA, SA and OA suggests a role of the LeY oligosaccharide in granulocyte traffic and inflammatory responses.

Reduced IL-2 expression upon antigen stimulation is accompanied by deficient IL-9 gene expression in T cells of patients with CVID.

Patients with common variable immunodeficiency (CVID) are heterogeneous in the clinical manifestation of the disease as well as in the underlying mechanisms leading to the immunodeficiency. In a previous study we identified a subgroup of patients with a primary immunodeficiency disease affecting IL-2 and IFN-gamma gene expression. The T cells of these patients revealed impaired proliferative response and reduced levels of IL-2 and IFN-gamma-specific mRNA after antigen stimulation in vitro, while cellular and molecular response to phorbol ester and the calcium ionophore ionomycin (PMA+IM) or anti-CD3 monoclonal antibodies (MoAbs) (OKT3) were comparable to those of healthy control individuals. Here we show that stimulation of these patients' T cells with tetanus toxoid (TT) resulted in dramatically reduced levels of IL-2, IL-9 and IFN-gamma mRNA, while IL-3 gene expression in three patients was comparable or even increased to the healthy controls. As expected, addition of exogenous IL-2 to tetanus toxoid pulsed cultures had virtually no effect on IL-2 transcription, but corrected the defect in IL-9 gene expression, while IFN-gamma mRNA levels were still reduced. In conclusion, these data suggest that recombinant IL-2 alone is not able to induce the IL-9 gene adequately in our patients, but clearly increases IL-9 mRNA levels in combination with tetanus toxoid.

T cell activity and cytokine production in X-linked agammaglobulinemia: implications for vaccination strategies.

In the 5 X-linked agammaglobulinemia (XLA) patients studied we show that memory T cells are present and that T lymphocytes proliferate normally to mitogens, monoclonal antibodies and, in particular, to recall antigens demonstrating normal in vivo T cell priming despite the absence of B cells. Furthermore, in vitro T cell activation in response to both T cell receptor-independent and T-cell receptor-dependent signals leads to a pattern of cytokine production characteristic of primed T cells and necessary for normal T cell function. These data are in good agreement with results obtained in gene-targeted mice and further support the concept that the absence of B cells does not impair induction of in vivo T cell memory and effector function which is generally considered to be of great importance in conferring protection against viral infections. Thus, while there is no risk of inducing infections in XLA patients by administering vaccines containing killed viruses or recombinant viral proteins, stimulation of T cell immunity by such vaccines may be of potential benefit particularly in the defense against infections with viruses such as the hepatitis B virus to which hypogammaglobulinemic patients are particularly exposed.

Local synthesis of C3 within the splenic lymphoid compartment can reconstitute the impaired immune response in C3-deficient mice.

Mice bearing a disrupted C3 locus (C3-/-) have an impaired Ab response to T-dependent Ags (bacteriophage phiX 174 and nuclear protein-keyhole limpet hemocyanin) characterized by a reduction in number and size of germinal centers and impaired retention of Ag by follicular dendritic cells. To test the importance of C3 synthesized locally within the lymphoid compartment during an immune response to T-dependent Ag, we reconstituted C3-/- mice with wild-type bone marrow of MHC-identical littermates. Engraftment not only restored local C3 synthesis in the spleen, but also rescued the impaired humoral response. The major source of C3 mRNA was MOMA-2+ macrophages localized within the white pulp areas of the spleen. Interestingly, C3 expression is apparently regulated as C3 mRNA was not detected in splenic sections of nonimmune mice. Furthermore, local C3 synthesis by donor macrophages reversed the impaired Ag trapping by splenic follicular dendritic cells in C3-deficient mice.