Objective—To determine functional characteristics of
monocytes obtained from cows with subclinical infection
with Mycobacterium avium subsp paratuberculosis
(MAP) that may have predisposed those cows to
becoming infected with MAP.
Sample Population—Monocytes obtained from 5
uninfected cows and 5 cows subclinically infected
with MAP in a herd with a high prevalence of paratuberculosis
(ie, Johne's disease).
Procedures—Monocytes from uninfected and subclinically
infected cows were incubated with MAP for
2, 6, 24, 72, or 96 hours. Variables measured included
expression of tumor necrosis factor-α (TNF-α), interleukin
(IL)-10, IL-12, transforming growth factor-β, and
suppressor of cytokine signaling-3 (SOCS-3); apoptosis
of monocytes; acidification of phagosomes; and
killing of MAP.
Results—Monocytes from infected cows had greater
expression of IL-10 and SOCS-3 at 2 hours of coincubation
with MAP and lower expression of TNF-α and
IL-12 when results for all incubation times were combined.
Monocytes from infected cows had a greater
capacity to acidify phagosomes. No differences were
observed in the rate of apoptosis or capacity of monocytes
to kill MAP organisms.
Conclusions and Clinical Relevance—Monocytes
obtained from cows with subclinical infection with
MAP had upregulated expression of IL-10 and
SOCS-3 within the first 2 hours after exposure to MAP
organisms. Although this did not inhibit acidification of
phagosomes, apoptosis of monocytes, or attenuation
of the capacity to kill MAP organisms, it may have
attenuated the capacity of mononuclear phagocytes to
initiate inflammatory and adaptive immune responses.
(Am J Vet Res 2005;66:1114–1120)
Objective—To determine cell membrane receptors involved in phagocytosis of Mycobacterium avium subsp paratuberculosis (MAP) organisms.
Sample Population—Monocytes were obtained from healthy adult Holstein dairy cows that were test negative for MAP infection on the basis of bacteriologic culture of feces and serologic test results.
Procedures—Monocytes or bovine macrophage cell line (BoMac) cells were incubated with MAP organisms for 30, 60, or 120 minutes with or without inhibitors of integrins, CD14, or mannose receptors. Phagocytosis was evaluated by light microscopy or by flow cytometry. CD11a/CD18, CD11b, and CD14 expression on monocytes and BoMac cells was evaluated by use of flow cytometry.
Results—Monocytes and BoMac cells rapidly phagocytized MAP organisms. However, compared with BoMac cells, monocytes had a greater total capacity to phagocytize MAP organisms. Addition of neutralizing anti-integrin antibodies (anti-CD11a/CD18 and anti-CD11b) substantially inhibited phagocytosis by monocytes during the first 60 minutes of incubation with MAP organisms, but were less effective at 120 minutes of incubation. Anti-CD11a/CD18 and anti-CD11b antibodies were less effective in inhibiting phagocytosis by BoMac cells. Addition of inhibitors of CD14 or mannose receptors also inhibited phagocytosis of MAP by monocytes. Addition of a combination of integrin and mannose inhibitors had an additive effect in reducing phagocytosis, but addition of integrin and CD14 inhibitors did not have an additive effect.
Conclusions and Clinical Relevance—Multiple receptors are involved in phagocytosis of MAP organisms. Although CD11/CD18 receptors appear to be the major receptors used by MAP at early time points, mannose receptors and CD14 also contribute substantially to phagocytosis.
Objective—To evaluate the role of the nuclear factor-κB (NF-κB) in the response of bovine monocytes to exposure to Mycobacterium avium subsp paratuberculosis (MAP).
Sample Population—Monocytes from healthy adult Holstein cows that were known to be negative for MAP infection.
Procedures—Monocytes were incubated with MAP organisms with or without a specific inhibitor of the NF-κB pathway (pyrrolidine dithiocarbamate), and activation of the NF-κB pathway was detected by use of an electrophorectic mobility shift assay. The capacities of monocytes to express tumor necrosis factor (TNF)-α, interleukin (IL)-10, and IL-12; to acidify phagosomes; to phagocytize and kill MAP organisms; and to undergo apoptosis were evaluated.
Results—Addition of MAP organisms to monocytes activated the NF-κB pathway as indicated by increased NF-κB–DNA binding. Addition of pyrrolidine dithiocarbamate prevented nuclear translocation of NF-κB, decreased expression of TNF-α and IL-10, and increased IL-12 expression. Treatment of MAP-exposed monocytes with pyrrolidine dithiocarbamate increased the rate of apoptosis but failed to alter phagosome acidification, organism uptake, or organism killing by those cells.
Conclusions and Clinical Relevance—Results indicated that NF-κB rapidly translocated to the nucleus after exposure of bovine monocytes to MAP organisms. These data suggest that NF-κB is involved in initiation of inflammatory cytokine transcription and inhibition of apoptosis but that it is not directly involved in phagosome acidification or organism killing.
Objective—To evaluate the role of the mitogen-activated protein kinase extracellular signal-regulated kinase (MAPKERK) pathway in the interaction between Mycobacterium avium subsp paratuberculosis (MAP) organisms and bovine monocytes.
Sample Population—Monocytes obtained from healthy adult Holstein dairy cows that were not infected with MAP organisms.
Procedures—Monocytes and MAP organisms were incubated together with or without a specific inhibitor of the MAPKERK pathway (PD98059), and the capacity of monocytes to express tumor necrosis factor alpha (TNF)-α and interleukin (IL)-10 and -12, produce nitric oxide, acidify phagosomes, kill MAP organisms, and undergo apoptosis was evaluated.
Results—The MAPKERK pathway was activated within 10 minutes after addition of MAP organisms to monocytes. Addition of PD98059 to monocyte-MAP mixtures decreased monocyte TNF-α and IL-12 mRNA expression but had no effect on IL-10 mRNA expression. Treatment with PD98059 failed to induce significant alterations in phagosome acidification, organism killing, nitric oxide production, or apoptosis of MAP-exposed monocytes.
Conclusions and Clinical Relevance—Results indicated that the MAPKERK pathway was activated during the interaction of MAP organisms with monocytes, which initiated TNF-α and IL-12 mRNA expression but failed to initiate antimicrobial activity. The MAPKERK pathway may be involved in initiating proinflammatory and proimmune responses in MAP infection in cattle.
Objective—To evaluate activation of Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) pathway in bovine monocytes after incubation with Mycobacterium avium subsp paratuberculosis (Mptb) organisms.
Procedures—Bovine monocytes were incubated with Mptb organisms with or without a specific inhibitor of the JNK/SAPK pathway (SP600125) for 2, 6, 24, or 72 hours. Expression of interleukin (IL)-1β, IL-10, IL-12, IL-18; transforming growth factor-β (TGF-β); and tumor necrosis factor-α (TNF-α) and the capacity of Mptb-infected monocytes to acidify phagosomes and kill Mptb organisms were evaluated. Phosphorylation status of JNK/SAPK was evaluated at 10, 30, and 60 minutes after Mptb incubation.
Results—Compared with uninfected control monocytes, Mptb-infected monocytes had increased expression of IL-10 at 2 and 6 hours after incubation and had increased expression of TNF-α, IL-1β, IL-18, and TGF-β at 2, 4, and 6 hours. Additionally, Mptb-infected monocytes had increased expression of IL-12 at 6 and 24 hours. Addition of SP600125 (specific chemical inhibitor of JNK/SAPK) resulted in a decrease in TNF-α expression at 2, 6, and 24 hours, compared with untreated Mptb-infected cells. Addition of SP600125 resulted in a decrease in TGF-β expression at 24 hours and an increase in IL-18 expression at 6 hours. Addition of SP600125 failed to alter phagosome acidification but did enhance the capacity of monocytes to kill Mptb organisms.
Conclusions and Clinical Relevance—Activation of JNK/SAPK may be an important mechanism used by Mptb to regulate cytokine expression in bovine monocytes for survival and to alter inflammatory and immune responses.