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Murine systemic lupus erythematosus The recent availability of two new strains of mice ( M R L / 1 and B X S B ) ~ which spontaneously develop a classical SLElike syndrome has added greatly to the potential value of murine SLE as an experimental model. Now this disease can be observed in mice of three quite different genetic backgrounds and essential immunopathological c o m m o n denominators of the disease indentified z. T h e origins a n d immunogenetic characteristics of the several SLE strains are very different. The New Zealand strains were derived from a n outbred stock by breeding for coat color over m a n y generations. The BXSB is a recombinant inbred strain derived from a single cross between a C 5 7 B L / 6 female and an S b / L male. The M R L / 1 has a complicated derivation but 75°70 of its genome is derived from LG, 13°7o from AKR, 12% from C3H and 0.3% fi'om C 5 7 B L / 6 (Ref. 1). All strains differ at their H-2 loci and, in addition, have significant differences among their various lymphocyte surface alloantigens and their lg allotypes. In each kind of mouse, the disease occurs in two forms, a late-life variety in which typical SLE develops in the second year of life and an early acute form in which the immunologic abnormalities present in the late-life disease ~oecome observable as early as one or two months of age a n d significant mortality occurs within the first six months of life (Fig. 1) ~. In the N Z B x W F 1 a sex difference determines the pace of the disease with the female developing early disease. In the BXSB strain the disease is similarly determined by sex. However, here the male develops early disease. T h e M R L / 1 mouse characterized by homozygous lymphoproliferative ([pr) genes has early disease in b o t h sexes but its congenic partner, the M R L / n which does not contain t h e / p r gene, develops the same disease in late-life.

Early in life in all strains of lupus mice there is an identifiable polyclonal B-cell hyperactivity which in some instances can be detected by one m o n t h of age. This B-cell hyperactivity is associated with a n u m b e r of immunologic abnormalities including: (1) hypergammaglobulinemia; (2) resistance to induction of tolerance; (3) increased numbers of lg secreting ceils; (4) increased numbers of cells spontaneously forming antibodies to incidental antigens and; (5) more relevant to the SLE, formation of a variety of autoantibodies including antibodies to nuclear antigens a n d to retroviral gp70. Significantly, no regulatory T-cell defects have been associated with this early B-cell hyperactivity. As a consequence of these a n d perhaps other immunopathogenic events, the animals of all strains with SLE develop circulating i m m u n e complexes, associated activation and depletion of serum complement with resultant glomeruloncphritis and vascular disease 3. An i m m u n e complex-induced degenerative arterial disease, until now little appreciated, is found in mice o[ all SLE strains, particularly in the coronary arteries where it is frequently associated with myocardial infarction. This lesion has many similarities to the coronary vascular disease of h u m a n s with lupus and suggests the possibility of a much wider role for i m m u n e complexes in degenerative arterial disease in general. In the F 1 progeny of the cross between the N Z W female and BXSB male, this coronary vascular change and myocardial i~nfarction is found in 80% of the male offspring and 30% of the females. While the clinical and m a n y of the immunopathologic features of routine SLE are similar in all affected strains, the particular constellation of a u t o i m m u n e responses varies a m o n g the several strains. Natural thymocytotoxic anti-


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Fig. 1. Mortality curves for late life and accelerated forms of SLE occurring in NZBxWFI~ BXSB and MRL mice


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bodies are conspicuous in the New Zealand strains but of little consequence in the BXSB and M R L / 1 , and some immunologically normal strains have levels as high as those found in thc New Z e a l a n d . Similarly, a n t i - r e d cell antibodies are conspicuous in the New Zealand Black and hybrid but not prominent in the other strains. Anti-Sm antibodies and rheumatoid factor are found in the M R L / 1 but not the other strains, and interestingly, only M R L / 1 mice have a rheumatoid arthritis-like disease. T h e pred o m i n a n t lymphoid cell type also varies with the different strains as does the reactivity of the lymphoid ceils against H-2-compatible targets, and also the role of the thymus, which is essential to the development of disease in the M R L / 1 and a modest restrainer of disease in the NZBxW. Finally, the influence of sex on the incidence and severity of the disease is strikingly different in the several strains. Studies of the inheritance of these various a u t o i m m u n e responses in recombinant inbred strains 4 or F 2 hybrid a n i m a l s 3 has i n d i c a t e d t h a t they are i n d e p e n d e n t l y inherited and independently expressed, strongly suggesting that there is no ' a u t o i m m u n e gene' which might predispose an individual to a wide variety of a u t o i m m u n e phenomena. In the absence of (1) a clear relationship between the M H C and SLE; a n d (2) a definite abnormality in general immunoregulation, it appears that murine SLE is in large part determined by a predisposition to make a n u m b e r of specific and independent a u t o i m m u n e responses. Analysis of the late-life lupus genetic background in hybrids derived from the several lupus strains indicates that there is no complementarity between the M R L mice and the BXSB and very little between the M R L and the two New Zealand strains. O n the other hand, the BXSB mouse complements the predisposition to lupus in both New Zealand strains, producing F~ hybrids quite similar to the traditional N Z B x N Z W mice. Accelerating factors quite different in each strain account

for the difference between late-life and early lupus. In the BXSB mouse, a Y chromosome-associated factor accelerates the onset of typical lupus in the male mouse. The Iymphoproliferative gene (Or) of the M R L similarly accounts not only for lymphoprolifcration but for a t r e m e n d o u s a c c e l e r a t i o n of the onset of disease in homozygous animals. In the New Zealand hybrid the female hormones apparently accelerate disease onset. T h e r e is little specificity in the relationship between the particular accelerating factor a n d the late-life lupus background affected since the Y chromosome-related accelerating effect of the BXSB operates equally effectively in male hybrid offspring from crosses with every other lupus mouse. Similarly, M u r p h y and Roths (personal communication) have found that the/pr gene will accelerate the disease in the NZB mouse as well as in the M R L mouse. Incidental events such as chronic L C M infection will significantly accelerate disease onset in all lupus strains. Thus, early severe SLE involves both a set of genetically-determined a u t o i m m u n e responses a n d an apparently nonspecific accelerator of endogenous or exogenous origin. FRANK J, DIXON

&'rz/)p~ Clinic and Research b'oun&llon, ka Jolla, CA 92037, U.S.A.

References 1 Murphy, E. D. and Roths, J. B. (1979) in Genelic Corzlrol of Autoimrrzune Disease, (Rose, N. R., Bigazzi, P. E. and Warner, N. L., eds) p. 207, Elsevier/North-Holland, Inc., New York 2 Andrews, B. S., Eisenberg, R. A., Theofilopoulos, A. N., Izui, S., Wilson, C. B., McConahey, P.J., Murphy, E. D., Roths, J. B. and Dixon, F.J. (1978),7. b2xp. Med. 148, 1198 3 Dixon, F. J., Theofilopoulos, A. N., lzui, S. and McConahey, P. J. (1980) in lrnmurzology 80, Fourth International Corlgress of I~nmunology, Progre.~s in Immunology IV, (Fougereau, M. and Dausset, J., eds) p. 959, Vol. 3, Academic Press, Inc. London 4 Raveche, E. S., Novotny, E. A., Hansen, C. r., Tjio, J. H. and Steinberg, A. D. (198l) J. Evp. Med. 153, 1187

Mast-cell secretion and structure-functional relationships of granule constituents and leukotrienes It is increasingly apparent that the interaction of the oxidative products of arachidonate with each other and with the mediators of the mast cell secretory granule may afford the intensity of local response needed for subclinical, homeostatic regulation of the microenvironment at cutaneous and mucosal surfaces and about venules that are regularly encroached upon by noxious substances *. In the mast cell, IgE-Fc receptor transmembrane-finked adenylate cyclase is activated upon immunologic challenge. A coupling protein, termed G / F protein or N protein in other studies, is presumed to respond to receptor perturbation and to ' R ' site agonists by a guanosine 5'-trip h o s p h a t e - d e p e n d e n t f u n c t i o n w h i c h a u g m e n t s the catalytic site activity ofadenylate cyclase. T h e transient rise in cyclic AMP, which is a result of activation of the a d e n y l a t e cyclase f u n c t i o n a l l y linked to the IgE-Fc receptor, is essential for mast-cell degranulation to occur. This is evidenced by the capacity of ribose modified adenosine agonists ('P' site) to inhibit release of mediators in a direct relationship to the attenuation of the transient rise in cyclic A M P which follows immunologic activation 2. The second messenger function of cyclic A M P in the mast

cell is carried out via the activation of cytoplasmic cyclic A M P - d e p e n d e n t protein kinases. Specific potentiation of receptor-linked adenylate cyclase, using an 'R,' site agonist (purine modified adenosine analog), increases mediator release, presumably via elevation of those cyclic A M P pools necessary for further activation of the protein kinases relevant to coupled activation and secretion. Elevation of cyclic A M P to levels far exceeding those produced by IgEFc receptor perturbation can also be achieved by phosphodiesterase inhibitors. Such non-specific cyclic A M P could have a negative effect on the release p h e n o m e n o n by leaving the cell depleted of cyclic A M P - d e p e n d e n t protein kinases at a critical time in response to immunologic challenge or by phosphorylation of an inhibitory protein. Thus, the role of cyclic A M P in mast-cell coupled activation and secretion is not unimodal as was once postulated. More importantly, there is a direct relationship between IgE receptor transmembrane-initiated activation of adenylate cyclase, generation of second messenger cyclic AMP, activation of cytoplasmic cyclic A M P - d e p e n d e n t protein kinase, and secretion of granule-associated mediators. Studies with dispersed a n d c o n c e n t r a t e d h u m a n

Murine systemic lupus erythematosus.

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