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Streptococcus pneumoniae cocultured with fibroblasts enhances both interferon production and cytotoxic activity by
Abstract:
Cell-mediated cytotoxicity against normal human fibroblasts was dependent on treatment of the fibroblasts with Streptococcus pneumoniae. Both spontaneous and interferon (IFN)-enhanced lymphocytes killed human foreskin (HFS) or skin muscle cells cocultured with S. pneumoniae five- to eightfold more than control nontreated cells. Based on Percoll gradient centrifugation, the cytotoxic effector cell migrated like a large granular lymphocyte. The human IFN produced from mixtures of HFS cells, lymphocytes, and S. pneumoniae was observed to be both a mixture of IFN-alpha and IFN-gamma and in an amount 500 times greater than that observed with lymphocytes on HFS cells alone, and it was in an amount 12 times greater than when lymphocytes and bacteria were cultured together. A mixture of antibodies to IFN-alpha and -gamma added to cocultures of fibroblasts and bacteria blocked the killing of fibroblast targets by lymphocytes (47 versus 13%). Thus, endogenously produced IFN was essential for the effective killing of the fibroblasts. Treatment of HFS cells with IFN before bacterial treatment protected the HFS cells from lysis by lymphocytes. The observation that normal diploid cells exposed to bacteria can be killed by lymphocytes suggests that natural cytotoxic cells are active at the site of bacterial infection and conceivably play roles in defense or pathogenesis.
Insights
Bacterial infection enhances natural cytotoxic cells to kill human fibroblasts. Endogenous interferon (IFN) production is crucial for this cell-mediated cytotoxicity, highlighting its role in immune defense.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Cell-mediated cytotoxicity plays a role in host defense against pathogens.
- The interaction between lymphocytes, fibroblasts, and bacteria in cytotoxicity is not fully understood.
- Interferon (IFN) is known to modulate immune responses.
Purpose of the Study:
- To investigate the role of Streptococcus pneumoniae in activating cell-mediated cytotoxicity against human fibroblasts.
- To determine the involvement of endogenous interferon (IFN) in this cytotoxic response.
- To identify the effector cells responsible for fibroblast lysis.
Main Methods:
- Co-culture of human fibroblasts (foreskin or skin muscle cells) with Streptococcus pneumoniae and lymphocytes.
- Assessment of cytotoxicity using lymphocyte killing assays.
- Characterization of effector cells via Percoll gradient centrifugation.
- Quantification of IFN-alpha and IFN-gamma production.
- Blocking experiments using antibodies against IFN-alpha and IFN-gamma.
Main Results:
- Streptococcus pneumoniae significantly enhanced lymphocyte-mediated cytotoxicity against human fibroblasts (5- to 8-fold increase).
- The primary cytotoxic effector cells were identified as large granular lymphocytes.
- Co-culture with S. pneumoniae led to a substantial increase in endogenous IFN production (IFN-alpha and IFN-gamma).
- Blocking antibodies against IFN-alpha and IFN-gamma abrogated the cytotoxic effect, demonstrating IFN's essential role.
- Pre-treatment of fibroblasts with IFN protected them from lymphocyte-mediated lysis.
Conclusions:
- Endogenously produced interferon is essential for effective cell-mediated killing of bacteria-exposed fibroblasts.
- Natural cytotoxic cells are activated at bacterial infection sites and may contribute to host defense or pathogenesis.
- The interplay between bacteria, fibroblasts, lymphocytes, and IFN is critical in this immune response.