Increased serum HLA class I molecule levels in elderly human responders to influenza vaccination

A potential role for shed soluble major histocompatibility class I molecules as modulators of neurite outgrowth

The neurobiological activities of classical major histocompatibility class I (MHCI) molecules are just beginning to be explored. To further examine MHCI's actions during the formation of neuronal connections, we cultured embryonic mouse retina explants a short distance from wildtype thalamic explants, or thalami from transgenic mice (termed “NSE-D^b”) whose neurons express higher levels of MHCI. While retina neurites extended to form connections with wildtype thalami, we were surprised to find that retina neurite outgrowth was very stunted in regions proximal to NSE-D^b thalamic explants, suggesting that a diffusible factor from these thalami inhibited retina neurite outgrowth. It has been long known that MHCI-expressing cells release soluble forms of MHCI (sMHCI) due to the shedding of intact MHCI molecules, as well as the alternative exon splicing of its heavy chain or the action proteases which cleave off it's transmembrane anchor. We show that the diffusible inhibitory factor from the NSE-D^b thalami is sMHCI. We also show that COS cells programmed to express murine MHCI release sMHCI that inhibits neurite outgrowth from nearby neurons in vitro. The neuroinhibitory effect of sMHCI could be blocked by lowering cAMP levels, suggesting that the neuronal MHCI receptor's signaling mechanism involves a cyclic nucleotide-dependent pathway. Our results suggest that MHCI may not only have neurobiological activity in its membrane-bound form, it may also influence local neurons as a soluble molecule. We discuss the involvement of complement proteins in generating sMHCI and new theoretical models of MHCI's biological activities in the nervous system.

Human leukocyte antigen polymorphisms: variable humoral immune responses to viral vaccines

Antibody formation in response to antigen stimulation remains the basis for measuring an individual's response and protection for most viral vaccines. A significant proportion of the variation in individual humoral immune response to vaccination appears to be genetic. The collection of genes found on chromosome 6 forming the human leukocyte antigen system provides one of the greatest sources of genetic variation in individuals with respect to their immunological responses. Recent research has demonstrated significant associations between vaccine response and human leukocyte antigen alleles. These associations not only explain why vaccine-induced humoral immune responses vary among individuals and between populations, but these variations may also hold the key to the development of future generations of vaccines.

Parasitic infection with Trichuris trichiura influences plasma levels of soluble HLA class I

High levels of sHLA-I (soluble HLA--class I) have been correlated with rejection episodes in solid organ transplant recipients and with graft versus host disease in bone marrow recipients. Studies of human infection with parasitic worms of the gut have suggested that certain individuals may be genetically predisposed to intense infection. In this study, the influence of parasitic helminth infection on levels of sHLA-I in plasma was investigated in 155 HLA typed individuals from St. Lucia, exposed to the gut parasite Trichuris trichiura. The results confirmed previous findings showing increased levels of sHLA-I in HLA-A9, and in this case HLA-A23 positive individuals. However, HLA-A9 positive individuals with high worm burden had significantly lower levels of sHLA-I in their plasma compared with HLA-A9 positive subjects with low worm burden. These results suggest that the intensity of T. trichiura infection influences the ability of HLA-A9 positive subjects to maintain high levels of sHLA-I.

Monitoring of soluble HLA class I size variants after liver transplantation

To monitor soluble HLA class I (sHLA-I) and their size variants after liver transplantation (LTX) plasma samples from 22 LTX patients were studied by sHLA-I ELISA, SDS-PAGE, and densitometry. Samples collected were classified into three groups: Group 1 comprised samples taken during episodes without complications, group 2 during episodes of cholangitis/cholestasis (CC), and group 3 during episodes of acute rejection (AR). Compared to group 1 (0.27 +/- 0.03 SEM microg/ml) mean sHLA-I increments in groups 2 and 3 were with 0.53 +/- 0.05 SEM microg/ml and 0.47 +/- 0.04 SEM microg/ml increased (p < 0.001). The same samples were studied by SDS-PAGE and the 43, 39, and 35 kD sHLA-I variants were quantified densitometrically. In samples of group 1 ratios of 43 vs. 39 kD bands revealed a mean of 2.1 +/- 0.3, whereas in group 2 and 3 these were only 0.8 +/- 0.1 SEM and 0.9 +/- 0.1 SEM, respectively, (p < 0.001). For the relation between 43 and 35 kD variants a reduced ratio of 1.1 +/- 0.2 SEM was confined to group 3 samples (p < 0.001), as groups 1 and 2 had ratios of 13.4 +/- 2.3 SEM and 8.4 +/- 2.9 SEM, respectively. This indicates that elevated sHLA-I levels during CC or AR are mainly caused by increases of 39 and/or 35 kD sized molecules. Therefore, our study demonstrates, that after LTX the contribution of sHLA-I size variants to total sHLA-I amounts changes drastically during immune activation pointing to different mechanisms of sHLA-I release.

Serum HLA class I levels in elderly humans. Utilization in following the response to influenza vaccine

Some healthy elderly people (30%-40%) do not respond to influenza vaccination. Subjects who respond to influenza vaccination show a significant increase in serum HLA class I levels 2 weeks after immunization. In the present study, serum HLA class I levels were measured prior to vaccination and 4 and 6 weeks after vaccination. The responders (HAI titers > or = 40) had higher prevaccination HLA class I levels (2.03 +/- 0.12 microgram/ml) than nonresponders (HAI titers < 40) (1.57 +/- 0.14 microgram/ml) (P = 0.03). The responders' sHLA levels remained stable at 4 (1.98 +/- 0.12 microgram/ml) and 6 (2.13 +/- 0.12 microgram/ml) weeks postvaccination. In contrast, nonresponders' sHLA levels increased at 4 weeks (1.85 +/- 0.18 microgram/ml) but declined to prevaccination levels at 6 weeks (1.59 +/- 0.16 microgram/ml). Lymphocytes isolated from the responders (n = 4) 4 weeks after vaccination had a higher in vitro proliferative response (mean SI = 20) than lymphocytes from nonresponders (n = 4, mean SI = 6.4) to the influenza vaccine. This proliferative response was significantly inhibited (mean SI = 6.3, P = 0.04) in the responders by the addition of an anti-HLA class I mAb and was associated with increased cell surface expression of HLA class I molecules. Two forms of sHLA class I molecules of relative mass of M(r) 42,000 and 40,000 were immunoprecipitated from the serum of nonresponders whereas only the M(r) 40,000 form was detected in the sera of young controls and of elderly responders.(ABSTRACT TRUNCATED AT 250 WORDS)