Autocrine versus lymphocyte-dependent mechanisms for macrophage activation

Alterations in lymphocyte function and relation to phospholipid composition after burn injury in humans

OBJECTIVE

Lymphocyte functions are dependent on fatty acid composition of membranes, and impaired functions can predispose patients to infection after burn injury. The current study was designed to describe changes in lymphocyte-phospholipid composition and lymphocyte-related immune functions from early to late recovery time points after burn injury.

DESIGN

Prospective observational.

SETTING

Firefighter's Burn Treatment Center, University of Alberta Hospital, Edmonton, Alberta, Canada.

PATIENTS

Subjects (n = 10) with >10% total body surface burn area.

MEASUREMENTS AND MAIN RESULTS

Blood was drawn from subjects at specific time points (0 days to >50 days) after burn injury. Fatty acid composition of the major phospholipid classes of isolated lymphocytes was determined by using gas liquid chromatography. Lymphocyte phenotypes and proliferation ([(3)H]-thymidine uptake and interleukin-2 and interferon-gamma production) in response to mitogens were determined. Lymphocyte phospholipid 20:4n-6 content was 30% to 60% lower early compared with late postburn time points (p <.001). Interferon-gamma production by stimulated cells was found to negatively correlate with n-3 content (r =.7, p =.008). The expression of CD25 on antigen-mature CD8+ cells was associated with higher proliferative responses (r =.88, p <.004). Proportion of CD8+ cells was lower, and the proportion of activated monocytes was higher early compared with late postburn (p <.05). Natural killer cell cytotoxicity was low early after burn and increased with recovery.

CONCLUSIONS

The results of this preliminary study suggest that immune activation occurs between the second and third week after burn injury, which is associated with changes in 20:4n-6 and n-3 fatty acid content of lymphocyte phospholipid. This study suggests that there is release or impaired synthesis of 20:4n-6 early after burn injury that may be related to functional changes in immune cells.

LPS stimulation of TNF-receptor deficient macrophages: a differential role for TNF-alpha autocrine signaling in the induction of cytokine and nitric oxide production

To evaluate the role of autocrine TNF-alpha signaling in macrophage activation, immortalized macrophages from normal mice (B6/J2) and from mice containing gene targeted disruptions of the type 1 and type 2 TNF-receptor genes (TRN) were stimulated under CD14-dependent or serum-free conditions. Although the B6/J2 and TRN clones mounted similar nitric oxide responses to LPS in the presence of serum, the TRN macrophages responded poorly when stimulated with LPS under serum free conditions. LPS stimulation of TRN and B6/J2 under serum-free conditions resulted in equivalent levels of IL-1beta, TNF-alpha, and iNOS gene expression. However, Western blot analysis revealed that iNOS protein production by TRN was 2-fold lower than that produced by B6/J2. These results indicate that autocrine TNF-alpha stimulation contributes to the signaling pathways initiated by ligation of LPS receptors in the absence of LBP and is involved in iNOS post-transcriptional regulation.