Summary Purpose:  To examine the role of innate immunity in a novel viral infection–induced seizure model. Methods:  C57BL/6 mice, mouse strains deficient in interleukin (IL)‐1RI, IL‐6, tumor necrosis factor (TNF)‐RI, or myeloid differentiation primary response gene 88 (MyD88), or transgenic mice (OT‐I) were infected with Theiler’s murine encephalomyelitis virus (TMEV) or were mock infected. Mice were followed for acute seizures. Tissues were examined for neuron loss, the presence of virus (viral RNA and antigen), perivascular cuffs, macrophages/microglia, and gliosis, and mRNA expression of IL‐1, TNF‐α, and IL‐6. Results:  IL‐1 does not play a major role in seizures, as IL‐1RI‐ and MyD88‐deficient mice displayed a comparable seizure frequency relative to controls. In contrast, TNF‐α and IL‐6 appear to be important in the development of seizures, as only 10% and 15% of TNF‐RI‐ and IL‐6‐deficient mice, respectively, showed signs of seizure activity. TNF‐α and IL‐6 mRNA levels also increased in mice with seizures. Inflammation (perivascular cuffs, macrophages/microglia, and gliosis) was greater in mice with seizures. OT‐I mice (virus persists) had a seizure rate that was comparable to controls (no viral persistence), thereby discounting a role for TMEV‐specific T cells in seizures. Discussion:  We have implicated the innate immune response to viral infection, specifically TNF‐α and IL‐6, and concomitant inflammatory changes in the brain as contributing to the development of acute seizures. This model is a potential infection‐driven model of mesial temporal lobe epilepsy with hippocampal sclerosis.

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Complement, part of the innate immune system, acts to remove pathogens and unwanted host material. Complement is known to function in all tissues, including the central nervous system (CNS). In this study, we demonstrated the importance of the complement system within the CNS in the development of behavioral seizures following Theiler's murine encephalomyelitis virus (TMEV) infection. C57BL/6 mice, deficient in complement component C3, developed significantly fewer behavioral seizures following TMEV infection, whereas mice depleted of complement component C3 in the periphery through treatment with cobra venom factor had a seizure rate comparable to that of control mice. These studies indicate that C3 participates in the induction of acute seizures during viral encephalitis.

We previously reported the discovery of a novel mammalian H1 linker histone termed H1FOO (formerly H1OO), a replacement H1, the expression of which is restricted to the growing/ maturing oocyte and to the zygote. The significance of this pre-embryonic H1 draws on its substantial orthologous conservation, singular structural attributes, selectivity for the germ cell lineage, prolonged nucleosomal residence, and apparent predominance among germ cell H1s. Herein, we report that the intronic, single-copy, five-exon (> or =5301 base pair) H1foo gene maps to chromosome 6 and that the corresponding primary H1foo transcript gives rise to two distinct, alternatively spliced mRNA species (H1foo(alpha) and H1foo(beta)). The expression of the oocytic H1FOO transcript and protein proved temporally coupled to the recruitment of resting primordial follicles into a developing primary follicular cohort and thus to the critical transition marking the onset of oocytic growth. The corresponding potential protein isoforms (H1FOO(alpha) and H1FOO(beta)), both nuclear localization sequence-endowed but export consensus sequence-free and possessing a significant net positive charge, localized primarily to perinucleolar heterochromatin in the oocytic germinal vesicle. Further investigation will be required to define the functional role of the H1FOO protein in the ordering of the chromatin of early mammalian development as well as its potential role in defining the primordial-to-primary follicle transition.