Characteristics of complement subcomponents C1r and C1s synthesized by Hep G2 cells

The association and activation states of complement subcomponents C1r and C1s biosynthesized by Hep G2 cells were studied. C1r and C1s are secreted in stoichiometric amounts; in the presence of Ca2+ they are associated in a complex that sediments similarly to plasma C1r2-C1s2. Both compounds are synthesized as monomer proteins of apparent Mr 86 000. C1r is secreted as a dimer. Secreted C1r is not autoactivatable but undergoes proteolysis by exogenous C1r; secreted C1s is also proteolysed by exogenous C1r. In the presence of immune-complex-bound C1q, secreted C1r and C1s are able to reconstitute C1, but normal activation requires extrinsic C1r2-C1s2.

Characterization of C1q, C1s and C-1 Inh synthesized by stimulated human monocytes in vitro

C1q, C1s and C1 Inh synthesized and secreted by human monocytes were characterized by SDS-PAGE. C1q is formed of three chains A (Mr approximately 35 000), B (Mr approximately 33 000) and C (Mr approximately 25 000) which are associated in two subunits A-B and C-C. It appears identical to C1q purified from plasma. C1s is secreted as a non-activated, monocatenar protein of Mr approximately 87 000 identical to proenzymic C1s from plasma. Secreted C1 Inh (Mr approximately 100 000) has a slightly higher Mr than purified plasmatic C1 Inh. Monensin treatment of the cells favours the intracytoplasmic accumulation of products at various glycosylation stages.

In vitro study of Fc-receptor function in autoimmune diseases

A simple test for studying in vitro Fc-receptor function of mononuclear phagocytes is described. Immune phagocytosis is analyzed as a dynamic phenomenon by using nearly pure suspensions of monocytes incubated for diverse times with autologous erythrocytes sensitized with highly purified IgG. In a series of normal volunteers and patients with vasculitis a strict correlation has been found between this in vitro assay and the measure of splenic clearance of IgG-coated red blood cells (RBC), the classical approach for studying in vivo macrophage Fc-receptor function by using sodium chromate 51Cr as tag. The use of this in vitro assay appears to be valuable mainly in cases requiring repeated measurements of Fc-receptor function for monitoring the course of disease or the effects of therapy.

Characterization of the C1q receptor on a human macrophage cell line, U937

The binding of C1q to the human macrophage cell line U937 has been studied. Fluorescence microscopy with fluorescein-conjugated F(ab')2 anti-C1q antibody showed that 100% of the cell population is able to bind exogenous C1q. Monomeric C1q binding to U937 cells is very weak at normal ionic strength (I0.15) and was therefore investigated at I0.07, conditions which stabilize the binding. However, aggregation of C1q on dextran sulphate or a lipid A-rich lipopolysaccharide allowed a firm, binding at I0.15. Quantitative binding studies with monomeric 125I-C1q showed a concentration-dependent, saturable, specific and reversible binding involving specific membrane receptors. Scatchard plots of C1q binding indicated [1.6 +/- 0.7 (1 S.D.)] X 10(6) sites per cell with an equilibrium constant of (2.9 +/- 1.8) X 10(7) M-1 at I0.07. The location of the molecule region mediating C1q binding was established with collagen-like fragments prepared by partial pepsin digestion, confirming earlier results obtained by inhibition studies.

Role of C3 in the control of monocyte C2 production

Serum-treated antigen-antibody complexes (IC) and DTSP-polymerized C3b and C3c inhibited the production of the second complement component (C2) by monocytes in culture, whereas monomeric C3, C3b, C3bi, C3c or C3d had no effect. The degree of inhibition of dithiobissuccinimidyl propionate (DTSP)-polymerized C3 was proportional to the degree of polymerization, dimer exhibiting less inhibitory activity than larger molecular weight polymers. The inhibitory effect of serum-treated IC and DTSP-polymerized C3b was abrogated by their pretreatment with Fab fragments of anti-C3, or pretreatment of monocytes with Fab fragments of antiserum to the C3b receptor (CR1). We have concluded that the inhibition of C2 production produced by serum-treated IC is due to bound C3b or C3bi, and is mediated by CR1. Furthermore cross linking of receptors is required for this effect; two or more than two receptors must be cross-linked for a significant effect to be observed.

[Role of immunoglobulins in the activation of complement]

Depending on their class and sub-class, immunoglobulins may activate the complement by the classical pathway or by the alternative pathway. This activating property depends on how immunoglobulins are associated. Activation by the classical pathway implies binding to, and activation of C1. Binding is essentially an ion type interaction between C1q and--in the case of human IgG's for instance--the C gamma 2 domain. It has recently been investigated in depth by various techniques, such as inhibition of the C1q--IgG interaction by chemical compounds or by peptides isolated from C gamma 2. Activation of C1 seems to involve some elements of C gamma 3. In addition to initiating the classical pathway, immunoglobulins may act as acceptors of the classical C3-convertase (C4b C2a); a structure accepting the newly formed C4b is present in the Fab portion of IgG. It would appear that optimal functioning of the complement system is achieved when the C1 activating site and the C3-convertase forming site are close together on the IgG molecule, since the newly born peptidic fragments have a very short life. Immunoglobulins may activate the alternative pathway via their Fab portion. This property is directly related to the ability of Ig's to accept nascent C3b, which probably includes that of accepting nascent C4b as described above. In the alternative pathway C3-convertase may form when structural conditions around IgG-bound C3b encourage binding of B to C3b rather than the intervention of I and H factors which degrade C3b. The Ig-C3b interaction responsible for activation of the alternative pathway may also be directly involved in solubilization of immune complexes during activation of complement.

Biosynthesis in vitro of complement subcomponents C1q, C1s and C1 inhibitor by resting and stimulated human monocytes

The capacity of cultured human monocytes to synthesize and to secrete the subcomponents of C1 and C1 inhibitor was examined. Non-stimulated monocytes secreted C1q and C1s from day 5 of culture. C1s reached a plateau immediately at its maximum level, whereas C1q secretion increased progressively until the end of the second week. Between day 12 and day 25, C1q secretion remained nearly constant (1-15 fmol/day per microgram of DNA, depending on the donor), whereas C1s secretion decreased and even in some cases stopped. C1r and C1 inhibitor were not secreted in detectable amounts by these resting cells. Stimulation of monocytes by yeasts, immunoglobulin G-opsonized sheep red blood cells or latex beads did not modify consistently C1q and C1s secretion. Activation by conditioned media from mitogen-, antigen- or allogeneic-stimulated lymphocyte cultures increased C1q production from 2 to 7 times and re-activated C1s secretion. Under the same conditions of activation, C1 inhibitor was secreted (up to 300 fmol/day per microgram of DNA) and C1r became detectable in culture supernatants. Isolated human monocytes are thus able to synthesize the whole C1 subcomponents; C1, if assembled, could be protected from non-immunological activation by locally produced C1 inhibitor. Activated monocytes appear to be a good tool for studying the assembly of C1 subcomponents and the role of C1 inhibitor in this process.

[Erythroblastopenia in a child with immune deficiency and hyper IgM]

The authors report the case of a boy with a history of recurrent infections, who presented with erythroblastopenia at age 5 years. An immune deficiency with hyper IgM was found. Erythroblastopenia appeared to be related to a serum inhibitor of erythropoiesis. This inhibitor was present in the serum IgM fraction and acts by blocking the erythropoietic activity of a soluble substance in the serum, which is not erythropoietin but which could be a cofactor of this hormone. A series of 5 plasma exchanges, performed in 10 days, permitted to clear the inhibitor and induced remission, still persisting after a 12 month follow-up.

[Cellular immunity in idiopathic nephrotic syndrome with minimal glomerular lesions and focal and segmental hyalinosis in children]

Cellular immunity was studied in 31 children presenting with idiopathic nephrotic syndrome (INS), of which 23 with minimal supposed or proven glomerular changes (MGC) and 8 with focal and segmental hyalinosis (FSH). In vivo, a clear hyporeactivity to the delayed hypersensitivity tests and decreased blood T lymphocytes, with a great dispersion of the values were found. Furthermore, such patients' sera display a factor inhibiting the proliferative response of the lymphocytes of patients and of control subjects, to non specific mitogens (PHA), both during exacerbation and remission periods. The hypotheses of an abnormality of cellular immunity and of the existence of an inhibitory factor in the serum of INS with MGC and FSH are discussed.

[Interactions between complement system and bacterial walls]

The complement system is involved in the antibacterial defence either with a delay, following the specific antibody response, or immediately through a direct interaction between complement components and the bacterial cell wall. Several gram- bacteria initiate the classical pathway through direct interaction between C1 and the lipid A of the lipopolysaccharides; this activation depends upon the structure, the accessibility and the state of polymerization of the lipopolysaccharides. Gram+ and gram- bacteria are able to activate the alternative pathway through a covalent C3b binding. Capsules appear to prevent activation due to their high content of sialic acid, which probably accounts for the virulence. As targets, bacteria may undergo opsonization mainly by C3b, or lysis through transmembrane channels formed by terminal components from C5b to C9.

Non-Hodgkin's malignant lymphomas: a cytologic classification based on statistical analysis and correlated with prognosis

On the basis of cytologic studies of 144 patients with non-Hodgkin's malignant lymphomas (NHML), a cytologic classification was established that was composed of three groups (1, 2 and 3) containing nine classes (1A, 1B, 1C; 2A, 2B, 2C; 3A, 3B, 3C). Statistical analyses were carried out using 52 well-defined elementary cytologic characteristics. All the results given by the data-gathering procedures (hierarchical and dynamic clustering methods), by the descriptive analyses (multifactorial and canonical analysis) and by the stepwise discriminant analysis were in agreement with the proposed cytologic classification system. The most discriminating cytologic characteristics of the classes were the cell size, the nuclear-cytoplasmic ratio, the degree of cytoplasmic basophilia, the homogeneity of the cytoplasm and the number of mitoses. The use of these properties renders this classification system reproducible and applicable to clinical practice. A comparison was made between the cytologic classes and the NHML patients as grouped according to their clinical courses. Of the patients in classes 2A, 2B and and 2C, 94% showed acute leukemic characteristics. Of those contained in classes 3A, 3B and 3C, 78% showed poor prognosis or metastatic patterns. Of those contained in classes 1A, 1B and 1C, 76% showed a good prognosis pattern.

[Biochemical data on C1 intrinsic activation (author's transl)]

C1 activation can be triggered by immune complexes and various effectors such as extrinsic proteases, bacterial or viral membranes, polyanions and polysaccharides. The basic mechanism of activation involves a limited proteolytic cleavage of C1r, with the generation of a proteolytic activity. Highly purified proenzymic C1r was obtained in high yield from human plasma by an indirect affinity chromatography step. Activation of isolated C1r in a fluid phase proceeded according to two distinct coexisting mechanisms: 1) an autocatalytic intradimer activation mediated by the pro-site of non-activated C1r; 2) an autocatalytic interdimer proteolysis triggered by nascent activated C1r formed in the course of the first reaction. DFP and C1-inhibitor did not have any effect on the first mechanism but were able to block the second mechanism. C1 activation is discussed in the light of recent results obtained by others from electron microscopy, and a tentative model is proposed.

[Agranulocytosis in the course of infectious mononucleosis. Demonstration of leukoagglutinins (author's transl)]

A case of agranulocytosis, quickly and spontaneously reversible, occurring in the fourth week of infectious mononucleosis in a 7-year old girl, is reported. The interest of the case lies in the importance of the symptomatology (jaundice, eruption, fever for 40 days), the serological detection of the role of the Epstein-Barr virus and, in particular, in the presence of leukoagglutinins judged to be responsible for the agranulocytosis.

[Lymphopenia and variations in T and B lymphocytes appearing immediately after irradiation (author's transl)]

Immunity tests were conducted in 21 patients with cancer, before and two months after irradiation. T and B lymphocyte counts were normal before irradiation when compared to a control group. Lymphopenia was present after irradiation affecting mainly the T lymphocytes (P = 0.005), whereas changes in B lymphocytes were not significant. These results suggest that irradiation has an immunosuppressive effect which should be studied in greater detail to establish possible therapeutic applications.

Quantitative study of T and B lymphocytes in Hodgkin's disease

Peripheral blood lymphocytes forming E rosettes in the presence of sheep red blood cells and those bearing surface immunoglobulins (SIg) have been studied quantitatively as an evaluation of T and B lymphocytes in Hodgkin's disease. 62 patients were investigated, 21 of whom before any treatment. It appears that the lymphocytes forming E rosettes are significantly lower in percentage in 86% of the patients and in absolute count in 65%. SIg bearing lymphocytes are elevated in percentile in 61% of the cases, but the absolute count is normal in 50% of the patients and elevated in 30% only. At diagnosis the T/B lymphocytes equilibrium is modified in 13 among 21 patients but, after the initial treatment of the disease, the ratio is modified in 90% of the patients in complete remission and remains unchanged for years even in the absence of relapse or immnunosuppressive treatment. It is suggested that SIg + lymphocytes from the peripheral blood are actually B lymphocytes and not anti-T-antibody coated T lymphocytes or antigen-antibody lacking of membrane markers, which are numerous in one third of the investigated patients, might be T lymphocytes with qualitative abnormality.

A human immunoglobulin in myeloma protein with anti-gastric parietal cell autoantigen activity

A previously characterised IgA Kappa myeloma protein was isolated and purified. The (Fab) alpha fragments of this immunoglobulin were obtained. The IgA and Fab fragments reacted in vitro with gastric parietal cells (GPC) using animal gastric sections and with smooth cytoplasmic membranes obtained from rabbit fundus (gastric) mucosa. This was seen macroscopically and by light and electron microscopy. Evidence is thus provided which supports the concept that this homogeneous immunoglobulin is a typical monoclonal autoantibody.

[Androgens and prolonged complete remissions in acute non lymphoblastic leukemias. Results of a systematic treatment with stanozolol associated with chemotherapy (author's transl)]

An androgen (stanozolol: 0,15 mg/kg/d) was systematically associated to the treatment of acute non lymphoblastic leukemias, since the beginning of induction therapy (vincristin, daunorubicin, prednisone) and throughout the maintenance period (6-mercaptopurine and methotrexate). Thirty-six patients less than 60 years old (median age: 44 years) presenting with acute non-lymphoblastic leukemia were entered to the study. Sixteen achieved complete remission (C.R.), i.e. 44% of the whole and 53% of treated patients. Out of 16 patients with complete remission, 4 relapsed during the observation period which lasted 4-1/2 years. The stability of the hematologic equilibrium in patients in C.R. is the main finding of the present study. The actuarial curve of the duration of the first complete remission reaches a "plateau"; after the 8th month only one relapse was observed in 9 patients. The rate of C.R. at 2 years is 76 +/- 23%. As compared to the results from other schedules of treatment, this rate appears significantly better, specially in the case of immunotherapy (p less than 0,001). A prospective randomized study is now suggested as to confirm this result; its therapeutic and theoretical basis and perspectives are discussed.