Th2-type responses function to generate particular antibodies, such as immunoglobulin E (IgE), which are important in the allergic response.
Th1-type immune responses function to generate cells and factors whose activity leads to cell death. 19, 20 The classes comprise distinct subsets of CD4 and CD8 T cells, produce a distinct set of cytokines and support different functions. Studies of the immune response have led to the delineation of at least two classes of T-cell response: T helper type 1 (Th1) and type 2 (Th2). The idea that the most important down-regulation of maternal immunity occurs locally at the maternal–fetal interface 14 – 18 has been used to reconcile these two bodies of evidence. However, contradictory older 8 – 11 and newer 12, 13 evidence also exists. Data exist from both old 1 – 4 and new 5 – 7 studies which suggest that down-regulation of maternal immunity occurs on a systemic level. Protection of the fetus from immune-mediated destruction is thought to rely on two main mechanisms: the maintenance of a barrier between mother and fetus and down-regulation of the maternal immune system. The fetal–placental unit is a semi-allogeneic graft that is in direct contact with maternal tissue, yet is normally not rejected by the maternal immune system. Other cytokines must be examined for their role in this phenomenon. The results suggest that IL-4-dependent Th2-type responses are not critical to maternal tolerance. The results show that: (1) deficiency in maternal IL-4 does not affect fertility, (2) deficiency in IL-4 is not associated with selective loss of male offspring in unimmunized mice, (3) pregnancy does not obliterate anti-H-Y reactivity in immunized mice and (4) maternal immunity to H-Y in the absence of IL-4 does not result in loss of male offspring. To help delineate the possible role of IL-4 in such maternal tolerance, female mice genetically deficient in IL-4 were studied. However, pregnant females immunized in this way do not deliver litters with fewer males. When injected with male spleen cells, female mice of certain strains mount a cytotoxic immune response to H-Y. This work focuses on maternal immunity to the male antigen H-Y, which is expressed in male fetuses. These responses rely heavily on interleukin-4 (IL-4) for both functions. One attempt to explain why the fetus is not generally rejected has been to suggest that during pregnancy Th2-type responses are dominant. In contrast, Th2-type responses support the production of non-cytotoxic antibody and suppress the Th1-type. T helper type 1 (Th1) responses support the generation of cellular cytotoxicity. At least two types of immune response are recognized. This however, does not usually lead to fetal loss. Hope this helps.Pregnant animals can generate and maintain immune responses to fetal antigens. Take these suggestions as general guidelines only since I can't see your entire topology. I can't see your entire topology, so there are variations on this theme that will provide a preferred design, but could require hardware purchases. For example if we were solving your problem (again, if I understand it), we might have layer 3 capabilities on switch 1 and 2 (where the servers connect) and leave switch 3 as a layer 2 device (for the clients). Spanning tree has limitations that can be overcome with a very stable layer 3 design. If I understand your topology and might consider adding layer 3 switching capabilities to your design. Just make sure switch 1 and switch 2 are the root and root+1 of the spanning tree domain and switch 3 will block on the uplink going towards switch 2 (run uplinkfast also). If you have enough bandwidth between switch 1 and switch 2, there is not a technical reason to worry about that issue. You might ask how critical that requirement is in this case. Suggest you read these links:Īs far as most direct path requirements you mentioned, spanning tree with triangle will not provide for that under the constraints you have listed (same VLAN). Which port is in spanning tree blocking state is determined by several factors to include the relative bridge priority for the VLAN in question on each switch. Therefore, one the three links between the three switches that are in the same VLAN must have a port in blocking state to prevent the loop. It is the job of spanning tree alogrithm to provide a loop-free topology. If the clients and all servers are in the same VLAN and you have three switches and three links (triangle), then you have an Ethernet loop.
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