To drive or be driven: the path of a mouse model of recurrent pregnancy loss.

This review is an example of the use of an animal model to try to understand the immune biology of pregnancy. A well-known model of recurrent spontaneous pregnancy loss is put in clinical, historical, and theoretical context, with emphasis on T cell biology.

Primary in vitro cytotoxic T cell response to non-major histocompatibility complex alloantigens in normal mice.

We have shown for the first time that it is possible to consistently generate a primary in vitro cytotoxic T cell (Tc) response to non-major histocompatibility complex alloantigens using responder cells from a normal mouse strain. This was achieved by carrying out, in the generating phase, a limiting dilution procedure in which it appears that suppressor cells that inhibit Tc activation or expansion are too dilute to manifest their effect. Moreover, the response was observed in mouse serum-(MS) as well as fetal calf serum- (FCS) supplemented media, an important finding in the light of the anomalous nonspecific effects induced by FCS. The cytotoxic response produced in MS-supplemented media was shown to be highly specific in both the generating and effector phases, whereas the responses in FCS had a strong nonspecific component.

Synthetic peptides as antigens and competitors in recognition by H-2-restricted cytolytic T cells specific for HLA.

The specificity of peptide recognition by a number of Kd-restricted CTL clones specific for HLA-CW3 or HLA-A24 was investigated. The CTL clones were derived from DBA/2 (H-2d) mice immunized with syngeneic P815 mouse cells transfected with genes encoding HLA-CW3 or HLA-A24 class I molecules. We had previously shown that CTL clones that lysed P815-CW3 transfectant target cells could lyse P815 (HLA-) target cells incubated with synthetic CW3 peptides corresponding to the COOH-terminal end of the alpha 2 domain. In the present study, we found that Kd-restricted CTL clones that lysed P815-A24 transfectant target cells recognized a synthetic peptide from the same region (residues 170-182) of the A24 molecule. CW3 and A24 differ by only one amino acid within this region. Recognition of CW3 or A24 peptides corresponded exactly with lysis of P815-HLA transfectants both for clones that mutually exclusively lysed CW3 or A24 transfectant target cells and for CW3/A24 crossreactive CTL clones. The latter CTL clones that lysed both CW3 and A24 transfectant target cells showed a clear preference for the peptide corresponding to the immunizing HLA allele. The homologous CW3 and A24 peptides could compete with each other for recognition, in contrast to a peptide from the same region of HLA-B7. Peptides from the corresponding region of the endogenous Kd and Dd/Ld molecules could also inhibit recognition of CW3 and A24 peptides. Competition with peptides apparently occurred at the level of the target cell. These results are consistent with a model whereby MHC class I molecules position protein fragments or peptides for specific recognition by T cells.

Analysis of cross-reactive antigen-specific T cell clones. Specific recognition of two major histocompatibility complex (MHC) and two non-MHC antigens by a single clone.

Two T cell clones, one specific for I-Es/d plus myelin basic protein (BP) and another specific for I-Ak plus influenza virus have been demonstrated to cross-react with DBA/2 cells. Genetic and serological analyses have shown that each clone recognizes its respective priming antigen in association with self-major histocompatibility complex (MHC) determinants and each recognizes DBA/2 minor H antigens in association with allo I-Ad MHC antigens. Further analysis of these clones suggests (a) that the allo I-Ad MHC epitopes recognized by these clones are not shared with self-I-A epitopes, (b) that the virus or BP antigens do not cross-react with DBA/2 minor H antigens, (c) that these clones recognize different determinants on the DBA/2 minor H antigens, and (d) that there is a requirement for a specific association between the different MHC antigens and the non-MHC antigens to stimulate these clones. This specific associative recognition argues strongly for the "altered self" hypothesis.

Antigenic modulation of Friend virus erythroleukemic cells in vitro by serum from mice with dormant erythroleukemia.

Friend leukemia virus (FLV) erythroleukemic cells cultured in medium containing FLV-immune serum from dormant FLV-infected mice undergo modulation of FLV cell surface antigens. Modulation was determined by an increased resistance to FLV antibody-mediated complement-dependent lysis and was associated temporally with the capping of FLV-immune complexes at the cell surface. Modulated cells regained their susceptibility to FLV antibody-mediated complement-dependent lysis when transferred to medium containing normal mouse serum. After 48 h of culture in FLV-immune serum, 26% of the FLV erythroleukemic cells were devoid of FLV cell surface antigens as demonstrated by immunofluoresence. Antigenic modulation occurred to a greater extent in cells maintained in logarithmic growth than in cells in GO or resting phase. FLV-antigenic modulation is discussed as a possible mechanism by which antibody induces and maintains FLV-transformed cells in a dormant state.

Inability of mice with a defect in B-lymphocyte maturation to respond to phosphorycholine on immunogenic carriers.

Mice with the CBA/N defect are unresponsive to the hapten phosphorylcholine (PC) even when presented on a variety of immunogenic carriers. Since these mice have the variable region gene for PC, their inability to respond may reflect deletion or suppression of the line of B lymphocytes which is responsible for the anti-PC response.

Prevention of type II collagen-induced arthritis by in vivo treatment with anti-L3T4.

The effect of in vivo administration of monoclonal anti-L3T4 antibody on the development of murine collagen-induced arthritis (CIA) was assessed. Treatment with anti-L3T4 resulted in a greater than 90% depletion of L3T4+ T cells in lymph nodes and spleen, an effect that appears entirely reversed 30 d after treatment. Administration of anti-L3T4 before immunization with type II collagen resulted in a significant decrease in arthritis incidence and delayed onset of the disease while treatment begun after a strong anticollagen IgG humoral response was underway was not effective in altering disease expression. These results suggest a prominent role for L3T4+ T cells in the pathogenesis of CIA.

Genetic control of immune responses in vitro. V. Stimulation of suppressor T cells in nonresponder mice by the terpolymer L-glutamic acid 60-L-alanine 30-L-tyrosine 10 (GAT).

In recent studies we have found that GAT not only fails to elicit a GAT-specific response in nonresponder mice but also specifically decreases the ability of nonresponder mice to develop a GAT-specific PFC response to a subsequent challenge with GAT bound to the immunogenic carrier, MBSA. Studies presented in this paper demonstrate that B cells from nonresponder, DBA/1 mice rendered unresponsive by GAT in vivo can respond in vitro to GAT-MBSA if exogenous, carrier-primed T cells are added to the cultures. The unresponsiveness was shown to be the result of impaired carrier-specific helper T-cell function in the spleen cells of GAT-primed mice. Spleen cells from GAT-primed mice specifically suppressed the GAT-specific PFC response of spleen cells from normal DBA/1 mice incubated with GAT-MBSA. This suppression was prevented by pretreatment of GAT-primed spleen cells with anti-theta serum plus C or X irradiation. Identification of the suppressor cells as T cells was confirmed by the demonstration that suppressor cells were confined to the fraction of the column-purified lymphocytes which contained theta-positive cells and a few non-Ig-bearing cells. The significance of these data to our understanding of Ir-gene regulation of the immune response is discussed.

Frequencies of mitogen-reactive B cells in the mouse. I. Distribution in different lymphoid organs from different inbred strains of mice at different ages.

Frequencies of mitogen-reactive B cells have been determined in vitro under culture conditions which allow every growth-inducible B cell to grow and mature into a clone of Ig-secreting PFC. The frequencies of LPS-reactive B cells in the spleen of 6- to 8-wk old mice were between 1 in 3 and 1 in 10 splenic B cells from the following inbred strains of mice: C3H/Tif; BALB/c; BALB/c nu/nu; C57BL/6J; DBA/2J; C57BL/6J x DBA/(2J)F(1); and CBA and A/J. Very similar frequencies are found for lipoprotein-reactive B cells in BALB/c, BALB/c nu/nu, C3H/Tif, and C3H/HeJ mice. No LPS-reactive cells but normal frequencies of lipoprotein-reactive cells were found in C3H/HeJ mice, genetically nonreactive to LPS. SJL mice had significantly lower frequencies of LPS- and of lipoprotein-reactive B cells (1 in approximately 30 B cells). The number of LPS- and of lipoprotein-reactive B cells in spleen was dependent upon the age of the mouse. Newborn spleen contained approximately 10 percent of the number of reactive cells found at 6- to 8-wk of age. From there the frequencies declined again to drop below 5 percent of the maximal number at ages beyond 11 mo. LPS-reactive B cells yielding IgM- and IgG-PFC responses could be found in mesenteric lymph nodes, bone marrow, thymus, thoracic duct, and peripheral blood of 6- to 8-wk old mice. Their frequencies were one in three to five lymph node cells, 1 in 50 to 100 bone marrow cells, one in 10(5) thymus cells, and 1 in 20 to 40 thoracic duct or peripheral blood cells.

Virus-triggered immune suppression in mice caused by virus-specific cytotoxic T cells.

Normal mice infected with 10(5) infectious doses of lymphocytic choriomeningitis virus (LCMV, WE isolate) generated a reduced or no T cell-independent IgM and/or T cell-dependent IgG response to a subsequent vesicular stomatitis virus Indiana (VSV-IND) injection; this transient immune suppression lasted for weeks to months. Connatally infected LCMV-carrier mice or acutely infected T cell-deficient nude mice had normal anti-VSV IgM and IgG or IgM responses respectively. LCMV-infected nude mice transfused with helper cell-depleted LCMV-specific immune spleen cells were immunosuppressed. Normal mice infected with LCMV but treated with a rat anti-CD8 mAb (that had been shown previously to eliminate cytotoxic T cells in vivo) and then infected with VSV exhibited a normal anti-VSV IgM and IgG response. Since no IFN-alpha or -beta was detected on, or after, day 6 of LCMV infection, neither LCMV alone, nor IFN induced by it caused the observed immune suppression; the presented evidence suggests that LCMV-immune CD8+ T cells were responsible for it. It is conceivable that a similar pathogenesis where virus-specific cytotoxic T cells may destroy virus-infected cells essentially involved in an immune response (APC, T helper cells, etc.) may be involved in other virally triggered immune suppression or in AIDS.

Differential tumor immunogenicity of DBA/2 mouse lymphoma L1210 and its sublines. III. Control of host resistance to drug-resistant L1210 sublines by H-2-linked and non-H-2-linked genes.

The effects of the host's genetic composition on the host's resistance to the DBA/2 L1210 lymphoma and three drug-resistant L1210 sublines (which show an increased expression of tumor-associated antigens) were investigated. Histocompatible F1 mice between DBA/2 and other mouse strains were given injections ip of graded numbers of these tumor cells, and a marked difference in the resistance of the host to tumor growth was demonstrated. The resistant hybrid mice showed markedly higher resistance to the L1210 sublines than to the L1210 parent lymphoma cells. Experiments with F1 mice between DBA/2 (H-2d) and certain congeneic intra-H-2 recombinant strains showed that the H-2b/d heterozygosity at the H-2K+l-A regions and additional non-H-2 genetic factor(s) confer the resistance to the F1 mice. The resistance was abolished by treating host animals with injections of silica, an antimacrophage agent, or rabbit anti-mouse thymocyte serum. These results suggest that the resistance is immunologic and that the genetically controlled host resistance may be directed to surface changes related to the increased expression of tumor-associated antigens.

Macrophage-mediated natural cytotoxicity of dimethyl sulfoxide-treated Friend erythroleukemia cells.

Dimethyl sulfoxide (DMSO) treatment of the Friend erythroleukemia cell line GM 979 markedly increased its susceptibility to natural cytotoxicity by splenocytes from normal inbred DBA/2 mice. Cytotoxicity occurred with normal adherent spleen cells as well as dextran-elicited peritoneal exudate (PE) cells but not with resident PE cells. Susceptibility of the leukemia cells to natural cytotoxicity increased to maximum levels upon treatment with 210 mM DMSO for 2-3 days. The natural cytotoxicity assayed by the 51Cr release procedure was first detectable after 9 hours of incubation and reached maximum levels by 24-30 hours. Although both DMSO and n-butyric acid induced rapid erythroid cell differentiation of the GM 979 cells, and both resulted in increased hemoglobin synthesis, only DMSO treatment enhanced the susceptibility of the cells to natural cytotoxicity by normal splenocytes. Cell-free supernatants from adherent spleen cells cocultured with DMSO-treated GM 979 cells for 6-15 hours were markedly cytotoxic for cultures of other chromium-labeled DMSO-treated leukemia cells. Supernatants from cultured adherent spleen cells alone, or lysates of DMSO-treated leukemia cells, did not possess cytotoxic activity. Resident peritoneal macrophages also had no cytotoxic activity against DMSO-treated cells, and culture supernatants from resident PE cells, even after incubation with DMSO-treated target cells, failed to show significant levels of cytotoxicity. These results indicate that normal splenic adherent cells as well as elicited PE cells have the ability to lyse DMSO-treated leukemia cells.

Distribution of radiolabeled alloantibodies in mice bearing 3-methylcholanthrene-induced sarcoma.

The distribution of purified 125I-labeled alloantibodies, prepared from the serum of DBA/2J mice obtained after immunization with C3H/HeJ spleen cells, was studied in immunosuppressed DBA/2J mice bearing either allogeneic C3H/HeJ 3-methylcholanthrene sarcomas growing s.c. or syngeneic SaD2 3-methylcholanthrene sarcomas. Once purified radiolabeled antibody was isolated from 125I-labeled immune gamma-globulin by a single adsorption onto C3H/HeJ RBC and elution from stroma prepared from these cells, by using 0.1 M glycine buffer (pH 3.0). Twice-purified alloantibody was then produced by Bio-Gel P-200 or Sephadex G-200 gel filtration chromatography or DEAE A-50 ion-exchange chromatography. In vitro, such purified antibodies bound specifically to C3H/HeJ RBC. In vivo, they localized to a significant extent following i.p. injection, preferentially in C3H/HeJ 3-methylcholanthrene sarcomas (4.4 to 8.9% of the injected dose per g of tumor equal to 1% of mouse weight), with mean tumor/blood ratios of 4.0 to 7.8, at 24 or 48 hr after injection. The percentage of injected dose localized in tumor and the tumor/blood ratio did not show significant differences with respect to time or method of antibody purification. Normal tissue/blood ratios in C3H/HeJ or SaD2 sarcoma-bearing mice were less than 0.9. The tumor/blood ratios in SaD2 sarcomas were approximately 0.6. Injection of 131I-labeled normal DBA/2J gamma-globulin resulted in normal tissue/blood and tumor/blood ratios of less than 0.9 in C3H/HeJ tumor-bearing mice.

Head-to-head comparison of protocol modifications for the generation of collagen-induced arthritis in a specific-pathogen free facility using DBA/1 mice.

Collagen-induced arthritis (CIA) is a widely used mouse model for studying inflammatory arthritis (IA). However, CIA induction protocols differ between laboratories, and direct comparison between protocol variations has not been reported. To address this issue, DBA/1 mice housed in conventional and specific-pathogen free (SPF) facilities were administered various combinations of two doses of collagen type II (CII) in complete (CFA) or incomplete Freund's adjuvant (IFA); some mice were also injected with lipopolysaccharide (LPS) and/or additional CII at specific intervals. Mice were evaluated for IA over the subsequent 2 months. Depending directly on the combination of CII, CFA, IFA, and LPS used, the incidence of IA ranged between 20%-100%, and severity extended from mild to severe even in an SPF environment. Our results demonstrate for the first time in head-to-head comparisons that specific variations in the use of CII, CFA, IFA, and LPS can induce a range of arthritic disease intensity and severity in an SPF facility. Thus, distinct experimental settings can be designed for robust assessment of factors that either exacerbate or inhibit arthritis pathogenesis. Furthermore, by achieving 100% incidence in an SPF facility, the protocols provide a practical and humane benefit by reducing the number of mice necessary for experimental assessment.

Suppression of genetic resistance to bone marrow grafts and natural killer activity by administration of fat emulsion.

Graft rejection is one of the major obstacles to successful bone marrow transplantation (BMT). If resistance to marrow grafting could be avoided, BMT could be used widely in treatment of hematological and immunological disorders. There has been evidence that natural killer (NK) cells play a major role in genetic resistance to BMT and that macrophages are also involved in genetic resistance. Agents toxic to macrophages such as silica and carrageenan have been found to have a suppressive effect on genetic resistance to BMT. Parenteral fat emulsions are known to accumulate in macrophages and to impair various functions of macrophages and those of the reticuloendothelial system. We show here that the administration of a fat emulsion, Intralipos 20%, to recipient mice can suppress genetic resistance to bone marrow grafts and NK cell activity probably through the impairment of the macrophage function. The administration of the fat emulsion might be a new tactic in conditioning protocols for human BMT in the future.

Characterization of monoclonal antibodies to the human thyrotropin receptor.

We have produced four monoclonal antibodies (mAbs), 34A, 49G, 11E7, and 12E3, which bind the human TSH receptor (hTSH-R) when expressed on a human thyroid cell line (GEJ), freshly dissociated human and murine thyroid cells, or Chinese hamster ovary cells stably transfected with the hTSH-R gene. These mAbs were obtained after immunization of DBA/1 mice with affinity-purified TSH-binding sites from GEJ cells. Biochemical studies, including sodium dodecyl sulfate-polyacrylamide-gel electrophoresis, Western blot, and immunoprecipitation of solubilized GEJ cell membranes or human thyroid cells showed that most of the mAbs recognized two bands: one located at 46-48 kilodaltons and the other at 86-88 kilodaltons. Inhibition of [125I]hTSH binding to solubilized porcine membranes (TSH-receptor auto-antikörper assay) or Chinese hamster ovary cell membranes previously transfected with hTSH-R gene showed that mAb 34A recognizes the hTSH-binding site of both receptors. In contrast, mAbs 49G, 11E7, and 12E3 recognize a structure located near the hTSH-binding site. Lastly, the ability of these mAbs to stimulate murine thyroid function was investigated by measuring cAMP production and iodide accumulation. The 34A mAb, which fully competes with [125I]TSH for binding to hTSH-R, was able to induce both functions. Conversely, the 12E3 mAb, which was the least potent inhibitor of [125I]TSH binding to hTSH-R-transfected cells had no effect. A relationship was, therefore, established between the capacity of mAb to hTSH-R to inhibit [125I]hTSH binding and their ability to induce thyroid functions.

Host age and H-2 tolerance in chimeric mice: mixed lymphocyte reactivity, cell-mediated lympholysis and responses to hapten-modified self.

In order to further our understanding of the reasons for the increased susceptibility of aged animals to autoimmunity, neoplasms and infectious diseases, experiments were performed to determine the ability of an aged environment to induce and support tolerance to major histocompatibility complex (MHC) determinants as well as to support the development of a specific immune response to modified self-determinants. The degree and mechanisms of tolerance to host and donor histocompatibility antigens were studied in bone marrow chimeras of the type (C57B1/6 X CBA)F1 leads to (C57B1/6 X DBA/2)F1 (BCF1 and BDF1, respectively). BCF1 bone marrow donors were 6 weeks old and BDF1 hosts were 18 months old at the time of chimerization. Four to ten months later, chimeras were found to fully tolerant to all three parental haplotyes and competent to respond to fourth-party strains as assessed in both mixed lymphocyte reactions and cell-mediated lympholysis. Tolerance to parental haplotypes could not be attributed to active suppression of reactivity. The aged host environment proved incapable of supporting the development of anti-modified self-reactivity as attested by the fact that neither the senescent BDF1 mice nor the BCF1 leads to BDF1 chimeras established in aged hosts could respond to trinitrophenol-modified autologous parental cells. In contrast, young BDF1 mice and BCF 1 leads to BDF1 chimeras established in young adult hosts were competent to respond to trinitrophenol-modified autologous and parental cells in an MHC restricted fashion. The significance of these results to the susceptibility of aged animals to intracellular parasitic infections and neoplasia is discussed.

In vivo mechanisms of alloreactivity. II. Allospecificity of cytotoxic T lymphocytes in sponge matrix allografts as determined by limiting dilution analysis.

We have examined the frequency and alloantigen specificity of CTL that accumulate in sponge allografts (sponges seeded with allogeneic splenocytes) in sponge isografts (sponges seeded with syngeneic splenocytes), and in splenocyte-free sponge implants. Using limiting dilution analysis (LDA), we observed that sponge isografts and splenocyte-free sponge implants from C57BL/6 (H-2b) mice usually acquire small numbers of CTL (less than 250 cells per graft) with DBA/2 (H-2d)-reactivity or C3H/HeJ (H-2k)-reactivity. These alloreactive CTL are not detectable in conventional 51Cr-release assays, presumably because they are too infrequent and/or because they are inactive CTL precursors. When we examined the accumulation of alloreactive CTL in sponge allografts, we observed that DBA/2 sponge allografts from C57BL/6 recipients accumulate 10 to 100 times more DBA/2-reactive CTL than alloantigen-free sponge grafts. Nonetheless, these donor-reactive CTL rarely constitute more than 0.5% of the T cells recovered from sponge allografts, even at the peak of the rejection response. This raises questions concerning the remaining 99.5% of the allograft-infiltrating T cells. We were unable to detect by LDA any host-reactive CTL in sponge allografts, thus excluding the possibility that some of the remaining T cells were host-reactive CTL of donor origin which diluted graft-reactive T cells. However, using LDA we did detect a significant number of third-party (C3H/HeJ)-reactive CTL in sponge allografts, suggesting that the intense immune response at a graft site might facilitate indiscriminate recruitment of T lymphocytes. Alternatively, this enhanced third-party alloreactivity might reflect the proliferation of donor-reactive CTL with incidental crossreactivity for C3H/HeJ alloantigens. While testing these two alternatives, we observed that LDA cultures designed to detect third-party-reactive CTL could also support the growth of the in vivo-activated, donor-reactive CTL from sponge allografts; This compromised enumeration by LDA of the less frequent, third-party-reactive CTL by LDA. Although LDA is the only method that detects the growing population of third-party-reactive CTL in sponge allografts, technical restraints exclude LDA as a method of determining whether donor-reactive CTL and third-party-reactive CTL are separate or overlapping CTL subpopulations. Hence, it remains unclear if third-party-reactive CTL are a significant or insignificant proportion of the CTL that infiltrate sponge allografts.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo mechanisms of alloreactivity. I. Frequency of donor-reactive cytotoxic T lymphocytes in sponge matrix allografts.

To study the development of alloreactive cytolytic T cells in vivo, C57BL/6 mice were implanted s.c. with polyurethane sponges bearing allogeneic (DBA/2) splenocytes. On various days thereafter, cells that had accumulated in these sponge grafts were tested for cytolytic activity against DBA/2 target cells in 51Cr-release assays, and for frequency of DBA/2-reactive CTL as determined by limiting dilution analysis (LDA). During these studies we found that LDA was consistently more efficient at detecting alloreactive CTL than the traditional 51Cr-release assays. As determined by LDA, sponge grafts initially infused with DBA/2 splenocytes acquired high levels of DBA/2-reactive CTL, while sponge grafts infused only with saline acquired few DBA/2-reactive CTL. DBA/2-reactive CTL first became detectable in sponge allografts approximately four days after implantation, and reached a maximal frequency by the 10th day after implantation. This frequency was maintained for at least the next seven days. In contrast, the ability of cellular infiltrates from sponge allografts to lyse DBA/2 target cells in 51Cr-release assays was not detectable until the 7th day after implantation, was optimal by the tenth day, but declined thereafter to lower levels, as observed on the 13th and 17th day after implantation. Since the frequency of CTL remains stable through the 17th day after implantation, this decline in cytolytic activity may indicate that donor-reactive CTL remain in sponge allografts, but they continue to differentiate to a noncytolytic status. We further observed that previous allosensitization with skin grafts markedly accelerates the accumulation of alloreactive CTL in sponge allografts. The mechanism that promotes more rapid accumulation of CTL in allosensitized sponge graft recipients remains to be established. Throughout these studies, we observed that even at peak development, donor reactive CTL are, at most, 0.2% of the cells recovered from sponge allografts. This raises some questions regarding not only the fundamental role of the CTL in allograft rejection, but also the role of the remaining 99.8% of the allograft-infiltrating cells.

Complement-dependent and independent mechanisms in acute antibody-mediated rejection of skin xenografts in the mouse.

Complement dependency of acute antibody-mediated rejection (AAR) was studied in a xenogeneic skin graft model in the mouse. PVG/c rat skin grafted to immunosuppressed mice was acutely destroyed by i.v. administered mouse anti-rat serum on day 7 after grafting. Depression of the hemolytic complement titer in the recipients was indicative for complement consumption during the rejection process. Complete and long-lasting complement depletion induced by treatment with cobra venom factor (COVF) decreased the sensitivity of the grafts to AAR. However, complete protection was not achieved, since high doses of antidonor serum again induced destruction. Similar results were obtained in C5-deficient recipients and in COVF-treated C5-deficient recipients. These results indicated that complement-independent rejection mechanisms were operative. This was further substantiated by the finding that purified noncomplement-fixing IgC1 subclass antibodies were able to elicit mice with a normal complement status was caused by intravascular coagulation without primary involvement of polymorphonuclear leukocytes. In complement-depleted animals an Arthus-like reaction was seen, with dense intravascular accumulation of polymorphonuclear leukocytes (PMNs) that, apparently, were attracted to the graft through complement-independent mechanisms.