MHC class-II-restricted antigen presentation by myelin basic protein-specific CD4+ T cells causes prolonged desensitization and outgrowth of CD4- responders.

T cells express MHC class II glycoproteins under various conditions of activation or inflammation. To assess whether T cell APC (T-APC) activity had long-term tolerogenic consequences, myelin basic protein (MBP)-specific rat T cells were induced to acquire MBP-derived I-A complexes to promote reciprocal antigen presentation. T-T antigen presentation caused extensive cell death among T-APC and MBP-specific T responders and caused long-term desensitization of surviving responders. Addition of the anti-I-A mAb OX6 to activated I-A+ responders inhibited T-APC activity, accelerated recovery from postactivation refractoriness, and prevented long-term loss of reactivity in responder T cells. Antigenic activation of responder T cells with irradiated T-APC induced profound losses in reactivity that lasted for over 1 month of propagation in IL-2 and was associated with preferential outgrowth of CD4- T cells. Antigen-activated CD4- T cells exhibited more rapid IL-2-dependent growth that eventually normalized compared to CD4+ T cells 1-2 months after antigen exposure. In conclusion, expression of T-APC activity by activated T cells represents an important negative feedback pathway that depletes antigen-reactive T cells and causes long-term desensitization of surviving T cells. Hence, T cell APC may be an important mechanism of self-tolerance.

Interleukin-2 promotes antigenic reactivity of rested T cells but prolongs the postactivational refractory phase of activated T cells.

IL-2 is a principal autocrine growth factor that promotes T-cell activation and proliferation. However, IL-2 has also been implicated as a key intermediate in the induction and maintenance of self-tolerance in vivo. The purpose of this study was to assess whether the differential regulatory activity of IL-2 was related to the activation status of responder T cells. In cultures of rested myelin basic protein (MBP)-specific T cells, IL-2 not only induced IL-2R alpha but also augmented surface expression of several other activation-associated glycoproteins including OX40, LFA-1, B7.1, B7.2, TCR, and CD4. Pretreatment of T cells with IL-2 also up-regulated subsequent antigen reactivity in assays of MBP-stimulated proliferation and IL-2 production and also promoted proliferative responsiveness to IL-2. In cultures of activated T cells, however, IL-2 inhibited subsequent reactivity to antigen or IL-2 and thereby prolonged a phase of postactivational refractoriness. Exposure of preactivated T cells to IL-2 also inhibited subsequent responses to the mitogenic combination of PMA, ionomycin, and IL-2 without enhancing cell death. These data support the concept that the inhibitory activity of IL-2 is dependent upon the activation status of T cells and is manifest as impaired cell cycle progression in response to a variety of IL-2-dependent stimuli.

Calcium-induced ERK activation in human T lymphocytes.

We have previously shown that stimulation of B lymphocytes with calcium ionophores lead to the phosphorylation and enzymatic activation of ERK2. We have now determined that stimulation of human primary and Jurkat T lymphocytes with ionomycin also results in the activation of ERK1 and 2 as determined by; shifts in the mobility of this enzyme on SDS PAGE gels, the binding of an antibody that recognizes only the activated form of this enzyme, and increased ability to phosphorylate myelin basic protein (MBP). Another calcium ionophore, A23187, also induced activation of ERK1 and 2 in human primary and Jurkat T lymphocytes demonstrating that this is a general effect of calcium ionophores and is not limited to ionomycin. The activation of ERK1 and 2 by calcium ionophores was rapid, transient, and occurred in a dose-dependent manner. Activation of ERK1 and 2 by increases in intracellular calcium were blocked by the MEK inhibitor PD98059. These data point to a new role for calcium fluxes in T lymphocytes.

Application of high-tech three-dimensional imaging and computer-generated models in complex facial reconstructions with vascularized bone grafts.

We present a series of six patients with eight flaps in whom computer-generated models were used for fabrication of vascularized bone grafts in complex facial restorations. Preoperative CT data, digitalized on tape, were converted by the CEMAX (Santa Clara, Calif.) 1500 Integrated Hardware and Software System to a three-dimensional visualization of the bone and soft-tissue deficiencies. These data were transmitted by direct computer link to a CNC milling machine that produced full-size slices "stacked" into a three-dimensional template. The acrylic replica aided selection of appropriate donor sites and intraoperative "carving" of bone transfers. Reconstructions included three zygomas, two maxillae, two mandibles, and one frontal bone. Donor sites were iliac crest, scapula, and outer calvarium. Four were free flaps and four island pedicle flaps. All healed without infection. Bone resorption was less than 10 percent. One flap was lost to thrombosis. Other complications included a transient facial palsy in one patient and temporary radial palsy from shoulder traction in another. Computer-generated templates for vascularized grafts are expensive and thus are not indicated or necessary in every patient. The advantages, however, are several. Custom models facilitate preoperative planning, with less guesswork of size, contour, and orientation of the graft, which is especially desirable with vascularized grafts, since the position of the pedicle is critical. Anesthesia time is decreased. Grafts can be fitted exactly, without reshaping and "nibbling." Nuances of depth and tapering are directly carved into the bone. By merging high-tech imaging and microsurgery, the best chance of optimal results can be achieved.

Palmaris brevis turnover flap as an adjunct to internal neurolysis of the chronically scarred median nerve in recurrent carpal tunnel syndrome.

Thirteen hands in 11 patients with previous carpal tunnel releases were treated by microscopic internal neurolysis and palmaris brevis "turnover" flaps. All patients in the series had positive electrodiagnostic testing, dysesthetic wrist pain, and numbness in the median nerve distribution before operation. Average age was 41.9 years (range, 27 to 62 years). Ten were male and 3 were female. Range of follow-up after the procedure was from 1 to 1 1/2 years. All hands with abnormal preoperative two-point discriminations or Semmes-Weinstein measurements showed numerical improvement in their sensory parameters. Thenar strength and bulk improved at least one grade in all six cases of thenar atrophy. Mean grip strength was 15.2% greater than before operation. Key pinch increased 5.5% and pulp pinch 31.9%. Subjective assessment of improvement ranged from 25% to 100%. All patients returned to their former jobs or to vocational retaining except the oldest patient who is semiretired.

The versatile temporoparietal fascial flap: adaptability to a variety of composite defects.

The unique properties of the temporoparietal fascial flap (TPFF) offer adaptability in reconstruction of a variety of composite defects. The broad, thin sheet of vascularized tissue may be transferred alone or as a carrier of subjacent bone or overlying skin and scalp. As a pedicled flap, it is ideal for defects of the orbital, malar, mandibular, and mastoid regions. As a free-tissue transfer, the large vessels and lack of bulk find broad utility in reconstruction of the extremities. This flap is our choice for reconstruction of the dorsal hand and non-weight-bearing surfaces of the foot. A viscous gliding surface decreases friction for tendon excursion. The thin contour is aesthetically superior to thicker flaps, allowing unmodified footwear or gloves. The pliable fascia convolutes into surface defects (e.g., bone craters) or drapes over skeletal frameworks (e.g., ear cartilage). The rich capillary network offers nutrition to saucerized bone, cartilage or tendon grafts, and overlying skin grafts. The geometry of the skull lends to fabrication of membranous bone for complex facial puzzles. The donor site is well disguised by hair growth. Twelve cases performed over a 2-year period demonstrate the versatility of this flap. These include complex foot reconstruction, ear and scalp avulsion, shotgun wound of the cheek and orbit, posttraumatic jaw recontouring, chronic osteomyelitis of the hand and foot, and acute resurfacing of dorsal hand with tendon reconstruction.

The "cap" technique: nonmicrosurgical reattachment of fingertip amputations.

With the exception of children, amputations at the level of the lunula survive poorly by direct reattachment. Microsurgical replantation is costly and often fails because of poor venous drainage. In a series of seven adult patients the severed tip was filleted and replaced as a "cap" over the skeletonized distal phalanx of the stump. A 2 mm remnant of germinal matrix was preserved for nail regrowth. The reconstructed digits, although shortened by an average of 6 mm, give the "illusion" of a normal finger. All were successful with small areas of tip necrosis in two, healing by secondary reepithelialization. Mean static two-point discrimination was 6.5 mm (range, 3 to 10 mm) and pulp pinch was 67% of normal. The "cap" technique of nonmicrosurgical reattachment is a simple, reliable method of functional preservation of pulp tissue, as well as normal esthetic appearance of the nail complex.

The reversed venous arterialized nerve graft in digital nerve reconstruction across scarred beds.

Conventional nerve grafts in complex digital injuries often yield poor results, particularly when placed in traumatized or avascular beds. Vascularized nerve grafts offer an option; experimental evidence suggests superior axonal regeneration across scarred beds with vascularized nerve grafts. We previously described a vascularized graft based on the dorsalis pedis artery--deep peroneal nerve "system." Reluctance to sacrifice this major artery, combined with the recent description by Townsend and Taylor and Gu, et al, of "reversed venous" arterialized nerve grafts, spurred us on to investigate the deep peroneal nerve--dorsalis pedis venae comitantes system. Fourteen neurovenous grafts were used in scarred or poorly vascularized beds for digital nerve reconstruction in 10 patients over a 4-year period. Graft length averaged 4.4 cm; interval from injury was 1 to 17 months. Sensory parameters of return included average static two-point discrimination of 8.3 mm, moving two-point discrimination of 5.8 mm, and median Semmes-Weinstein monofilament appreciation of 2.83. Two patients received three vascularized grafts and three conventional grafts for adjacent nerve injuries in the same digit, serving as internal controls. In these patients, the vascularized nerve grafts returned mean static two-point discrimination values of 9.3 mm and moving two-point discrimination values of 6.7 mm. The conventional nerve grafts averaged static two-point discrimination of 14.3 mm and moving two-point discrimination values of 10.3 mm. These differences imply enhanced axonal regeneration through vascularized nerve grafts. These data suggest that the reversed neurovenous graft may be the procedure of choice in secondary reconstruction of digital nerves across scarred beds or following injuries with poor soft-tissue vascularity, especially in those patients with cold intolerance.

Microsurgical management of complex fingertip injuries: comparison to conventional skin grafting.

In selected cases of severe fingertip injuries, an aggressive approach using microvascular and microneural techniques can yield functional results equal or superior to conventional methods of treatment in less severe injuries. A series of 20 patients were treated microsurgically from 1983 to 1986 for severe acute distal finger injuries or their early sequelae--five distal replantations, eight neurovascular free tissue transfers, and nine distal neurorrhaphies/nerve grafts with or without vascular conduit. Concurrently, 33 simpler tip avulsions were treated with full-thickness skin grafts for comparison. In the microsurgical series, one replant and the distal 1 cm of a free toe flap necrosed. Replants averaged two-point discrimination of 9.8 mm and pulp pinch 65 percent of normal; free toe transfers, two-point of 6 mm, pulp pinch 58 percent; distal nerve reconstruction, two-point 6 mm. Operating time per digit averaged 5.0 hours for replants, 4.3 hours for toe flaps, and 1.5 hours for nerve repair/grafts. All patients returned to full pre-injury employment within six months. None required revisional surgery for dysesthetic fingertips. In the conventional skin graft series, greater than six months follow-up is available in 17 patients. Average two-point was 7 mm (range: 3 to greater than 15 mm) and pulp pinch 83 percent of normal. There were seven poor results with cold intolerance, numbness, and paresthesias, three of which required revisional surgery. The data suggest that microsurgical management of fingertip injuries achieves results comparable to skin grafts, despite the greater complexity of the initial injury. This approach has resulted in fewer secondary tip revisions. Operative times are acceptable. Parameters of sensory return are similar, although pulp pinch is slightly less. Disability times are comparable to the average in major pulp losses. Of importance, final permanent partial factors of disability are diminished in rating, due to retained digital length, improved esthetic appearance, and less dysesthesia/cold intolerance.

Microsurgical application of freeze-dried venous allografts.

Freeze-dried venous interposition allografts with an internal diameter of 1.0 mm and a length of 1.0 cm were placed into the femoral arteries of 17 Sprague-Dawley albino male rats in order to investigate patency and host tissue response. The immediate patency rate was 88%. The epigastric island flap was monitored as a sign of patency in the early postoperative period (defined as 1 to 3 days). Twelve of the 17 subjects were observed for 2 months, at which point 66% (8/12) remained patent. There were two aneurysmal dilatations. Histopathological studies and transmission electron microscopy demonstrated that freeze-dried veins undergo complete remodeling in vivo by a normal reparative process and that they do not induce a cellular immune response in the host.