GM-CSF expression

GM-CSF is undetectable in the serum of normal humans, and no normal cells have been shown to express this protein constitutively. Some transformed cells may constitutively express GM-CSF, and it is actively synthesised and secreted by antigen- and lectin-stimulated T cells and by endothelial cells and fibroblasts exposed to TNF, IL-1 or endotoxin. Other sources of GM-CSF include stimulated B lymphocytes, macrophages, mast cells and osteoblasts, whilst TNF and IL-1 can stimulate its production by acute myeloid leukaemia cells. Some solid tumours and synovial cells from rheumatoid joints may also express GM-CSF and this may be important in disease pathology. 

Regulation of expression may occur at both the transcriptional and post-transcriptional levels. The mRNA for GM-CSF contains (in common with those of some other cytokines) conserved regulatory sequences in the 3 untranslated region, which may affect its rate of translation. The gene is constitutively transcribed in monocytes, endothelial cells and fibroblasts, but the mRNA is unstable and so does not accumulate to levels sufficient to allow translation into significant amounts of protein. Activation of these cells results in the increased expression of GM-CSF protein, which arises from both an enhanced rate of transcription (as detected in nuclear runoff experiments) and also an increased stability of the mRNA, perhaps by mechanisms analogous to those described above during activation of G-CSF expression ( 2.2.3.1). 

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Gollner G, Aman MJ, Steffens HP, et al. Interferon-a (IPN-a) inhibits granulocyte-macrophage colony stimulating factor (GM-CSF) expression at the post-transcriptional level in murine bone marrow stromal cells. Br J Haematol 1995 91 8-14. 

Sharpe S, Hanke T, Tinsley-Bown A, et al. (2003). Mucosal immunization with PLGA-microencapsulated DNA primes a SIV-specific CTL response revealed by boosting with cognate recombinant modified vaccinia virus Ankara. Virol. 313 13-21. Kusakabe K-I, Xin K-Q, Katoh H, et al. (2000). The timing of GM-CSF expression plasmid administration influences the Thl/Th2 response induced by an HI V-l-specific DNA vaccine. J. Immunol. 164 3102-3111. 

GM-CSF demonstrated induction of a systemic immune response and regression of established tumor. Consistent with the postulated mechanism, GM-CSF expression induced the accumulation of DCs at the tumor site (259). Clinical studies using GM-CSF transduced tumors have shown encouraging preliminary results in melanoma (260) and renal cell (261,262) and prostate (263) carcinomas, and studies in lung cancer are underway. 

Ou-Yang, P. et al., Co-delivery of GM-CSF gene enhances the immune responses of hepatitis C viral core protein-expressing DNA vaccine Role of dendritic cells, J. Med. Virol., 66, 320, 2002. 

G-CSF expression is controlled at both the transcriptional and posttranscrip-tional levels. A sequence of 300 nucleotides upstream of the initiation codon is conserved in both the murine and human genes, and this appears to contain three regulatory sites. G-CSF (and some other cytokine genes) may be constitutively transcribed by cells such as blood monocytes, fibroblasts and endothelial cells, but the mRNA may be short-lived (fi/2 < 15 min). The mRNA contains poly-AUUUA sequences in the untranslated region, and this motif is usually associated with mRNA instability. Indeed, such regions have also been identified in mRNA for GM-CSF, IL-1, IL-6, interferons, TNF, some growth factors, c-jun, c-fos, c-myc and c-myb. Upon the addi-... 

Recombinant GM-CSF (produced in Escherichia coli, yeast or COS cells) has been tested for its ability to affect haematopoiesis in primates and humans. Because of its relatively short half-life in the circulation, daily administration (usually via intravenous infusion) is required. Administration results in a transient neutropenia, monocytopenia and eosinopenia within 30 min of administration, presumably because of the ability of GM-CSF to stimulate the expression of adhesins and hence increase the numbers of leukocytes adhered to the capillary endothelium in the marginated pool. Additionally, these leukocytes may accumulate in the lungs after GM-CSF administration, which may contribute to the decrease in the observed numbers... 

In addition to its effects on haematopoietic cells, GM-CSF can also affect the function of mature cells. GM-CSF treatment increases the survival, cytotoxicity and eicosanoid formation by eosinophils, and can increase the tu-mouricidal activity, cytokine expression, surface antigen expression and oxidative metabolism of macrophages. It is chemotactic for endothelial cells, can induce the proliferation of some tumour cells, stimulates histamine release from basophils and affects the viability and function of Langerhans cells. Its effects on mature neutrophils are described in 7.2.1, 7.3.4. 

IL-1, which has no proliferative effect when acting alone but modulates the responses of haematopoietic cells to other CSFs (possibly by enhancing CSF-receptor expression), enhances the differentiation and survival of early progenitor cells observed in response to IL-3 and stimulates the production of G- and GM-CSF by T lymphocytes, endothelial cells, macrophages and fibroblasts ... 

A large number of cytokines generated during an inflammatory response can affect neutrophil function. Some of these cytokines, such as G-CSF and GM-CSF, can affect the rate of biosynthesis of mature neutrophils in the bone marrow they can also affect the function of mature cells by priming certain functions (such as the respiratory burst, degranulation and expression of some plasma membrane receptors). These effects are described in detail in Chapters 2 and 7, respectively the present chapter briefly describes some the properties of cytokines known to affect the function of mature neutrophils. 

FcyRIII is actively synthesised by blood neutrophils, and its rate of expression can be increased up to twofold after exposure of neutrophils to GM-CSF ( 7.3.3). It is also shed from the membrane during activation by,... 

Figure 7.4. Up-regulation of CR3 expression during priming. Neutrophils were incubated in the absence (unprimed) or presence (primed) of 50 U/ml GM-CSF for 60 min at.37 °C. After this incubation, expression of CD lib and CD 18 was measured by FACS analysis, using the method described in Edwards et al. (1990).

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